Q is not necessarily true virtualization. It is actually an emulator, but Intel Macs do take advantage of a "Virtualizer" giving a big speed boost, but it is still x86-on-x86 emulation.
See here:
http://www.kju-app.org/proj/wiki/KjuVirtualizer
Therefore, it's not in direct competition with Parallels because Parallels take advantage of Intel's virtualization technology built into their chips, Q does not. In my experience trying out Q, it feels just like Virtual PC did, no where near as fast as Parallels.
I do agree, try out Q before you outright buy Parallels. It's fine for checking sites in IE. But if you need a real solution to run Windows on your Mac, Parallels can't be beat (yet).
Q Gives You Mac Virtualization for Free - And It Works