Fedora Core 6 has some new desktop effects with that release are nicely implemented. Sure it is eye candy, but it is done in an elegant way which you are likely to leave switched on because it is not too distracting. For an example of what I mean, take a look at this video on YouTube:
Naturally you are going to want to have a pretty decent machine to run these effects. The "Windows Wobble when Moved" effect in particular is quite resource-hungry and a little slow on my work machine (a Pentium 4 but with integrated graphics, yuk!), but I just have that switched off and everything else enabled. You will never go back to the old way once you see this running, it's great!
Updated 2021 : note that the above post is out of date as it was originally published in 2007, but is left here for archival purposes.