Discovery of the day: Macs are utterly unusable without a mouse. There's no notion of keyboard-selected focus, anywhere. After trying out random keystrokes for the better portion of 5 minutes, I think that every web browser on OSX is completely missing this functionality. This is particularly bad for dialogs, since OSX also decided to skip the whole underline-the-shortcut-key in dialog boxes. Your only discoverable options are to accept the default, or hit escape. That's not really empowering the user. :(
This came out of an attempt to update an unpatched Mac Mini that (at the time of my arrival on the scene) had no mouse. Logging in was easy enough, as was launching applications (yay, spotlight!), but then I needed to authenticate with the wireless so the Mac Mini could actually download the updates in question. And I couldn't find a way to click the darned "Log In" button without a mouse. Eventually I stole the one from the computer next to me, but I was frustrated on principle. After all the talk of how "easy-to-use" Macs are, I throw one quirky setup at it and it fails miserably.
Then as soon as Software Update had run, I saw why the system wasn't patched: it had 2GB of disk free, and needed some 7GB free to apply the patch. A little du(1)-fu discovered that the entire disk was full of a former grad student's video editing clips. Since I didn't know if it was safe to delete the lot, I opted instead to gzip all the giant files up (bzip2 would take waaaay too long) and then see if I could do the patches one at a time. This seems to be working.