I've been running various developer builds of Tiger (from ADC) on my "secondary" machine - the desktop box that I use as "communication central". It's been so absolutely solid that I haven't even had the chance to file any bugs on it!
Now that it's been released, I'll be installing the final build of Tiger on that box first thing on Monday, and will attempt the full XCode + WebObjects + Subversion install. If all is happy, I'll be installing Tiger onto the laptop (my primary/development system) at first chance. That's the only part of the install that has me concerned. If WO works, I'm laughing!
I absolutely LOVE the new Mail.app (I'm less offended by the new Mail UI than many others, apparently, and the Smart Folders do kick so much ass! I have a Smart Folder that says something like: "All messages that are flagged, and have come from anyone on the Pachyderm project in the last 2 weeks") Spotlight is cool, and Dashboard is unbelievably useful (moreso than Konfabulator is, IMO, and I paid for that).
Initial rumours about WebObjects development on Tiger is that it basically works, but is a bit quirky. There is also an update making its way toward release (5.2.4 - a whopping .0.1 update in over a year!) which will possibly take care of those quirks.
Java 1.5 is also available for MacOSX 10.4, but I don't care either way about that at the moment - I'm using a whole bunch of Java 1.4 stuff, and don't really want to go chasing down minor tweaks and niggles introduced by 1.5