The MBP is about a month old now and in the last few days (ever since WOPR's 100% happy thread actually) I've had a few problems with user switching, powering down and putting it to sleep. It's not consistent, but happens once or twice a day. The computer will not shut down or restart, forcing a hard power down. Once it hasn't let me log out as a user. Once it hasn't gone to sleep properly (oscillating sleep light comes on, but fan is running and the case is extremely hot with the lid closed - on opening the lid the power light is on but the screen is dead - again a hard power down was needed).
I've also noticed that the machine is running much hotter now than it did in the first couple of weeks that I had it. Could it be related to 10.4.6? In the old days I'd have tried repairing permissions but now John Gruber tells us it's all voodoo, and anyway since 10.4.6 it's been telling me that nothing needs repairing.
edit - forgot also to mention the Finder crashing a couple of times.