Also, I finally figured out something that was annoying the crap out of me for the past few weeks, which I will post on separately for reference, but wanted to note here as well: I was having intermittent, maddening tearing issues under 10.6 on my home theater mini, and I couldn't figure out why. Turns out it was because the mini was booting when its only video device (the TV) was powered down and therefore unrecognized. This was triggering "headless" mode or something of the sort, and basically Quartz Extreme was failing to initialize. This, in turn, disabled coalesced video writes, which in turn caused tearing (it also, I believe, caused drastically worsened video performance when upscaling video in some apps, QT player most notably).
Glad I've finally pinned that down, though it's looking like I'm going to need to boot/restart the thing with the TV on to prevent this, since a Detect Displays isn't good enough.
(I don't think this is new with 10.6, either, just that I noticed it after the upgrade; I remember having CoverFlow fail when I'd booted headless before, for the same reason.)