Sorry, missed your comments yesterday. Very droll.
But UAC in Vista is NOT a problem for me. For Windows I think it's part of the solution. And several Linux distros use a UAC-like feature (at least some of them not as safely implemented in their default settings as Vista's, imo) to deal with the issue of someone trying to accomplish a task from within a user account that doesn't have the permissions needed.
UAC pops up when I'm issuing commands through the GUI -- at precisely the moment I would expect it to pop up. It doesn't interrupt me while I'm typing a document or working on a spreadsheet or database because a download over a slow connection finally finished. And it doesn't accidentally cause me to perform an action or dismiss a dialog just because I was entering data or clicking a mouse button at the moment it happened to pop up. Used properly UAC allows me to do virtually 100% of my work in Vista while logged on to a standard or restricted user account, invoking admin privileges only when they are needed. This was something Windows needed desperately.
Applications which actually stack up multiple modal dialog windows on me don't stay installed on any of my systems. And I've seen that crap on Linux, too. It's generally a sign that something about the offending app or the OS is misconfigured and failing. Or, if talking about a browser, it's a sign that I've gone to a very badly written Web site. I've never seen IE7 or recent Firefox versions succumb to such behavior..
As for simians, the software I use in Vista, even some of it which steals focus, is, on the whole, rather well-written -- not showing much evidence of having been written by millions of furry, feces flinging little fellows toiling at their keyboards. It's just that the GUI mavens in many companies have, for some reason, fallen in love with this idiotic idea that focus stealing is good. It's rather like trying to have a conversation with a group of adults, one of whom has a petulant, nasty little brat constantly circling about and whining and blowing snot on people's knees and interrupting the conversation. That parent should teach said little crawler to signal quietly from the corner of the room and to await patiently the parent's attentions. (I'm talking about having the the frikkin' software use the notification area, in case the software developers aren't getting the gist of my little story.)
I use Vista/XP/2000/NT4 (deity, help me), Ubuntu, Linux Mint, OpenBSD, AIX, and Solaris. Haven't spent enough time at the "desktop" in BSD, so don't know whether or not focus stealing happens or is possible there. Never seen it in AIX or Solaris, but use them for very specific single-application work. I like Vista and Linux Mint the most out of all of these as multi-tasking desktop systems. Both of them prompt me for permission when permission is needed. But neither of them should allow somebody's crappy little snot-encrusted crumb snatcher to yank on my pants leg while I'm pouring a martini, nipping an hors d'oeuvre, and chatting up my wife. But, occasionally, they do.
A warning to software developers: I have a shovel and am intimately familiar with large areas of wilderness in North America. It's unlikely anyone would miss you, anyway.