While I'm fairly new to the Mac, I learned the hard way in the Windows world that it does not pay to be the guinea pig on new operating systems or major upgrades. No matter how thoroughly something has been tested there always seem to be glitches and conflicts that have to be fixed and somehow they seem to wind up on my computer. So I think I'll let others be ahead of the curve on this one and wait a couple of months to let things shake out. In the meanwhile, I find Leopard 10.5.8 to be perfectly adequate, especially when compared to Windows.
That thinking doesn't always apply, at least not to companies with proper software development cycles for their OS.
At Sun, for example, the way things worked was that any bugs reported in the current release of Solaris were *always* fixed in the development release first, then backported as patches to earlier releases if appropriate or desired. So, when you installed Solaris 10 FCS, you got all the bug fixes that had been reported up until the code freeze point, so you should have a more stable release.
I hazard a guess that MacOS development works in a similar way. Yes, there will be new features, or major rewrites of sub-systems or applications (Finder in the case of Snow Leopard), which does have a bearing.