It's impressive how things have turned around for Apple, a few years back the company had a bigger share of the overall PC market however most Windows users wouldn't consider switching to a Mac or even showed desire to move to a "closed" system... nowadays Apple has become a niche however it's continued desire to innovate has brought a lot of attention to them.
One of our recent polls showed exactly that, users were asked if they would at least try Mac OS X for the PC if that actually existed, results were pretty favorable for Apple's OS.
PearPC is a rough approximation of a G3 chip, which was used in Macs a couple of generations old. The emulator is missing the chip's Floating Point Unit, which can greatly accelerate many multimedia tasks, like video playback.
The piece of software was released last week and it still on its early stages however it does run already some software made for PowerPC machines, including of course, Apple's Mac OS X (painfully slow we hear).