The iMac spawned a plastic revolution
When Apple introduced the translucent colored plastic all-in-one iMac in 1998, it started a styling trend (or fad depending on your point of view). The "bondi blue" machine sold 800,000 units in the first 139 days, and not long after, scanners, speakers, USB hubs, and a plethora of other components began to come out in translucent colored plastics, obviously aping the iMac. (Not to mention the new Deluxe George Foreman Grill that popped up in Super Bowl ads.) Eventually, a handful of PC makers, including eMachines, began selling systems that went so far in copying the look of the iMac that Apple sued.
Nowadays, companies are following in the styling trail Apple blazed with the iMac, though not quite so closely. You find translucent plastic highlights on machines from HP and others. Compaq has made radical advances in their case looks, especially with their iPAQ, and even hyper-conservative Dell has released a two-tone gray Dimension 8100. Apple shattered the beige mold for home PCs, and newer looks are and will continue to supplant beige.
Another area where Apple has innovated in case design is in easy access. Most Apple case designs use no screws for opening the case, opting instead for latches. With the first several generations of PCI PowerMacs, Apple put the power supply on hinges, allowing easier access to the motherboard. Apple later added a one-button method of unlatching the side of the case. Dell has recently added those two features into their new machine, the Dimension 8100. Design ideas that start in the OEM market tend to filter down to the component market, so we expect standalone PC cases to start integrating these features as well.
An open PowerMac G4 case with the motherboard easily accessible
Apple has taken their easy access design ideas even further with their current cases. They feature a hinge mounted case side that opens via a screwless latch. The motherboard actually lies on the hinged side of the case, which means that, when the case is opened, the motherboard has nothing blocking access to it. This makes it extremely easy to access the memory, PCI, and AGP slots. It's almost as easy as just sitting your system on a motherboard tray without the rest of the case, just as we have it in our test lab.