The answer is ironing bugs :P.

And trust me, you wouldn't want to use it if there were show stopping bugs. Kinda like when I use the alpha and beta versions of the next Ubuntu releases (Hardy Heron right now). It's real irritating when an update breaks something and you have to fix it manually (track down whatever it is, fix it).

And that's with my desktop and laptop which dual boot. I can't even imagine doing that with my tablet which only runs one OS at the moment (though I guess if you also booted off MMC..)