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It can invigorate a company's image or squander its brand equity. To see which gambles paid off, Fortune turned to a few experts to judge some of the most dramatic transformations.

Apple - A Chic Redesign

Talk about a makeover.

Just imagine what an iBook or iPhone would look like with this image on it: definitely not as chic.Ronald Wayne designed Apple's original logo in 1976 when the company was still operating out of a garage.

It shows Isaac Newton sitting beneath a tree with an apple dangling precariously above his head.

Rob Janoff used the same apple in his redesign a year later.

"You can almost feel the '70s and '80s taking place when you take a look at that rainbow apple," says Bill Gardner, principal of Gardner Design.

Apple dropped the multi-colored logo in 1998 for a monochromatic version, produced in every color imaginable, until transitioning it to today's popular shade of chrome.

BP - Re-Branding Faces Reality

After British Petroleum merged with Amoco, the oil giant commissioned branding firm Landor & Associates and advertising agency Oglivy & Mather to fashion a corporate identity that would convey the image of a forward-thinking, socially conscious company.

BP had already begun building that persona: After all, former CEO Lord John Browne was the first oil executive to acknowledge the threat of global warming.

The bursting green, yellow, and white Greek mythology-inspired "Helios" symbol that replaced BP's shield is meant to imply a shift toward alternative, environmentally-friendly sources of energy like solar and biofuels, and relentless advertising has made the company's initials synonymous with "beyond petroleum."

But a series of oil spills and accidents suggested that BP wasn't walking the walk, leading some to consider its wildly successful mark more a mask than its true face.

"If the story doesn't hold up, the mark and the brand start to lose their luster," says Brendán Murphy, senior partner at Lippinott, a brand management firm.

IBM - Simply Classic

In 1972, IBM ditched its original logo in favor of the symbol it has used ever since.

In an attempt to update its antiquated look -- the old logo wrapped the words "International Business Machines" around an image of the globe -- IBM tried two different block-letter logos before legendary branding designer Paul Rand created the current version.

In this modern design, the lines that make up the letters represent "speed and dynamism," according to the company.

They owned the lines going through it before everyone started using lines," Gardner says. And because of its simplicity and originality, "you have a hard time desiring to mess with it."

Kraft Foods - Mismanaged and Indistinct

The association with fattening products like Kraft Macaroni & Cheese -- and negative connotations stemming from its connection to tobacco conglomerate Philip Morris -- tainted both Kraft's corporate history and its logo. So it made sense that just under two years after Altria (formerly Philip Morris) spun off shares of Kraft to form a distinct company called Kraft Foods, the food giant would want to revamp its image.

But it wasn't necessarily a success: While the slimmer styling suggests healthier products, many analysts consider the new logo, by Nitro design agency, a disaster. Introduced in February, it's already been altered, with changes to both the location and shape of the ambiguous "flavor burst," which evokes both butterflies and flowers.

"I don't get a story from it," Belk says. "The fact that they changed it twice in such a short period of time says that they're not managing it very well. They're not taking a strategic approach to it." What's more, the new logo bears an uncanny resemblance to Yoplait's, which isn't even a Kraft brand.

Procter & Gamble - No Devil Inside

The logo P&G used when it launched in 1851 pictured a man in the moon with 13 stars, representing the original American colonies -- à la the original U.S. flag. But critics later claimed the stars connected to form "666" and that the curls were in the shape of devilish sixes as well.

P&G chopped off the old man's bearded curls in 1991, and then two years later, the company trashed the pictorial logo altogether for the simple initials it uses today. "While it's unfortunate that they had to change for the reasons they did," Murphy says, "I think the 'P&G' logo is a strong mark."

Starbucks - Song of the Siren

Here's one Starbucks concoction many hoped had disappeared a long time ago. The brown logo featuring a nude siren had been the company's icon since 1971, when it was developed by Starbucks co-founder Terry Heckler.

In 1992, it was updated to the green logo used today, picturing a less exposed siren. But in May of last year, the brown logo -- with the breasts covered -- made a comeback for several months during a promotion. Even with the minor touch-up, the flashback was not met with much enthusiasm.The retro logo "goes from nostalgic to crude," says Belk, whose opinion was shared by many.

UPS - Modern and Traditional

In 2003, as UPS moved into the digital age -- from packaging and shipping to managing logistics, too -- the company outgrew its 42-year-old iconic logo. Celebrated in the design community for its connection to legendary designer Rand, the original logo and its old-fashioned bow gestured to the company's roots in neighborhood package delivery. "It had a humor and a humanity to it," Murphy says.

But the new logo represents a strategic decision to emphasize UPS's expanded business operations, and analysts also praised the company's FutureBrand designers for nodding to UPS's heritage by preserving the shield, keeping it lighthearted, and leveraging the color brown. "You would never think [brown] would be an asset," Belk says, "but in their case, it is."

Wal-Mart - Softening Its Image

Wal-Mart didn't always make its employees as smiley as the happy face that rolled back prices on its commercials. "They were known as a heartless, soulless company that didn't care about people -- even their own people," Belk says.

But Wal-Mart's 2008 branding makeover by Lippicott produced a logo that now conjures up the image of an "inviting and accessible" store, explains Belk, rather than the "daunting and monolithic" one the old logo (in use since 1992) projected.

The redesign transformed the big-box store's name to one word, used standard capitalization and a softer shade of blue, and added a yellow spark symbol. The new logo, like the company's updated tagline -- "Save Money. Live Better." -- invigorates the company with an "altruistic mission," says Belk, as it expands its reach from rural America to an urban consumer.

Xerox - X Misses the Spot

It's so painful for me to even look at that thing," says Gardner about Xerox's new logo, which the company unveiled last year. Xerox decided to lose its signature 'X' logo in hopes of changing its reputation for being just a copier and printing company as it increases its focus on software and services.

But analysts and customers have been critical of the redesign -- Xerox's biggest makeover in forty years. "The new logo is first and foremost a sphere...and the less obvious 'X' is almost an afterthought," says Gardner. "Xerox owns the letter 'X' in the corporate world. Why would they want to bury the 'X' instead of making the most of it?"

The company stands behind its decision, however, saying in a press release that the new look is "more lively" and the 'X' in the ball represents the company's connections to customers, partners, industry and innovation.