Mac OS X 10.6.4 is released. Full details here. Combo update here.
10.6.4 just came out this morning and I quickly updated. The reason was that since installing 10.6.3 two months ago, I've had this really bad problem where when I resume from standby, the screen's back light doesn't turn on and I have to manually change screen brightness to make it light up. Sometimes though, even doing that doesn't work, and I have to close the lid and re-open, sometimes multiple times, until the screen works again.
After upgrading, the problem seems to have disappeared.