The Cupertino, Calif.-based company insists the blemishes are not defects but lines formed through the normal course of manufacturing. Some industrial designers agree this could be the case.

But Mac enthusiasts buying the Cube in part for its looks may be sorely disappointed by the hair-thin lines, which typically form around two rivets on top of the Cube, the DVD drive and the Apple logo on the system's front.

Industrial designers also warn that only in real-world use will the company be able to tell for certain the nature of the lines. At issue is polycarbonate plastic--the same material used in some eyeglasses--and how it flows and cools when injected in a mold.

Phil Schiller, Apple's vice president of worldwide product marketing, made the company's position clear.

"We are not aware of--and I don't believe there is any issue with--the longevity of the material and anything becoming or emerging as a weakness or crack over time," he said. "There is no information that we have that that's the case."

That may not mollify Cube buyers irked by flaws in the system's clear casing. Mac newsgroups have been rife with commentary on the issue, as have discussion threads on Apple's support Web site.

And Schiller acknowledged the lines "do show up as a top support-call driver. People do ask a lot about it. There's no doubt about it."

While many callers are relieved to find their Cubes aren't defective, Apple is still embroiled in an embarrassing situation over a system sold as much on appearance as function.

"Apple has done an outstanding job in making the investment in industrial design and cosmetics. Hats off to them," said Malcolm Smith, vice president of development for industrial designer Flextronics. "So to them, I'm sure it's a catastrophic event if they're having cosmetic problems."

The G4 Cube is one of the smallest fully functional computers available, measuring about 8 inches square and 10 inches high in an enclosure of clear plastic.

"In a stylish design like this, people are paying for style. And apparent cracks aren't style," said Gartner analyst Chris LeTocq.

Part of Apple's problem is the nature of the material it uses to make the G4 Cube's crystal-clear enclosure.

"The materials they have chosen are probably the right ones," Smith said. "In fact, your choices are quite limited if you want to have that crystal-clear look. Polycarbonate is an outstanding material in general."

The process Apple uses to make the Cube case is called injection molding, where molten plastic flows through a mold and fills in around openings for various parts, such as screws or the DVD drive.

"When the plastic flows around stuff and comes back together, the coming together of the plastic can form a visible seam line. That's a part of the injection molding process," Schiller said.

Schiller insisted these seam, or mold, lines are typical for the process but are more noticeable because of the thickness of the plastic and Apple's decision to polish it to optical-grade clearness.

"Because of this you can notice the mold lines more than on any other plastic part we know of made on this planet," Schiller said. "We work really hard to minimize them, but it's impossible to have none."

Apple's support Web site deals with the mold lines in a cursory manner, referring to them as "normal" and "not cracks."

But the mold lines that appear are not exclusive to the G4 Cube. Apple also has reported instances of similar lines on iBook. The lines also have been reported in the Harmon Kardon speakers bundled with the G4 Cube and Apple's 22-inch flat-panel Cinema Display.

One thing supporting Apple's contention that the lines are more cosmetic than structural is the consistency with which they appear in the same places, mainly around the rivets and near the end of the DVD drive slot.

On the other hand, some of the lines can be felt with the hand, noted one message poster on Apple's support site. "These cracks that I am referring to are not mold lines--they are cracks," the person wrote. "You can see them, feel them, watch them grow."

The Cube's unusual square design and the amount of stress placed on the enclosure by the weight of the hardware could lead to fractures over time, a problem stemming from the materials used and the injection molding process. Whether that is happening in this instance or will happen in the future is uncertain, Smith said. Only time will tell.

"There are two reasons you get cracking," he explained. "There's stress in the plastic, and that stress gets there from the assembly--if you're screwing something to it or overstressing the part in its application--or there's stress that gets molded into the product itself."

Schiller insists the lines are not cracks and there will not be any in the future.

"Is there a systemic issue that causes anything other than mold lines? Not that we know of," he said.

Still, unhappy customers have been asking for replacement enclosures or Cubes, and with good reason, said Technology Business Research analyst Tim Deal.

"The Cube relies almost entirely on its appearance, and it is designed for its appeal," he said. "That's the name of the game with Apple. They're all about design and appearance. You can't promote a product off its design and appearance and have flaws with it, then sweep it under the rug as being normal."

Those Apple customers looking to vent or seek additional help from the company's online support site may be surprised at their options. In a posting yesterday, the Power Mac moderator directed all problems to customer relations and away from the support site.

The moderator added: "Forewarning that additional posts on this topic will likely be removed unless they contribute new information to the topic. You are welcome to post your opinions and other comments to any of the third-party hosted discussion forums."