There are certainly issues with Vista, I'm not arguing that there are not. But from my experience (Running public Betas and release candidates daily since August 06), this is the most stable windows client MS has released. It certainly is the easiest installation I've done - though as a rule, I never do upgrade installations. I always backup my data, wipe the drive and do a clean install from the get go. SO I can't speak to users who have had trouble with upgrade installations. I had enough issues with upgrades under 9x that I gave up the practice. I use my Vista system everyday, and honestly have only had a single crash of the OS, under Release candidate 1, which was months ago. There have been hiccups with applications, but part of being active in the beta testing was to send automated reports back to MS. I knew what I was getting myself into, and it wasn't anywhere near as bad as I had originally anticipated.
Early adoption certainly isn't for everyone, but much of the grumbling I've been hearing (and I'm not being specific to these boards) sounds eerily familiar to the early days of XP, and 95. As Chad mentioned, MS has the disadvantage (compared to Apple) of making their OS run under a ridiculous number of hardware configs, with a fairly impressive amount of backwards compatibility. They could hold back the release another year, and still have major technical hurdles upon launch. I'm of the belief that sooner or later, they have to ship it and get ready for the hotfixes and service packs. And nothing will prepare them for this better than getting it out to "real world" users.
I like the interface tweaks, I like the ease of networking config. I'm happy with the state of the OS this early after public release. That said, I would still not recommend it to the average windows user. Driver support and application compatibility being the main reasons. If you are a big time PC gamer and have a lot of titles that depend on openGL, then I would have to say don't even think about it, as the implementation is not particularly good, compared to what is already available under XP.