I've been using the WWDV Developer Preview (Build 10A380) for two days now as my main OS. It's been extremely stable thus far. With that said, make sure you do make a backup of everything if you do decide to run Snow Leopard. Apps in Snow Leopard launch faster than they do in Leopard and everything does feel snappier.
There were a few problems I ran into however.
-iStat Menubar does not work. The Dashboard widget still works, but the menubar utility does not. I have contacted the maker of iStat, and they are going to release a Snow Leopard compatible version in a few weeks.
-Quicktime X has no Preferences menu. This isn't a big deal though. VLC still works for most of the movies I have to play.
-Vuze does not work with Snow Leopard. I have been using uTorrent for Mac until a Snow Leopard compatible version of Vuze is released.
-My MacBook Pro had to be shut down via the holding the power button once. The only time was right after installing Snow Leopard. It has shut down fine ever since.
-SoundSource menu bar item does not work. I'm certain that all these menu bar apps will work once they have been updated for Snow Leopard. I'm using the default volume control now.
Other than that, it's a really sweet update to Leopard and I can't wait until the official release comes out in September.
Here's a picture of my desktop. It doesn't show much, but I think the new Quicktime X icon is worth taking a look at. It's cool.
All you have to do is burn the image to a DL DVD.. or you can put it on your external hard drive or a partition in your main hard drive and install from there. It doesn't wipe data. Just a painless upgrade. It took about a half hour for me running it off my iPod.
Edit: Sims 3 is hanging at random points under Snow Leopard. The only way to fix that is to hold the power button. :-/