Well, I downloaded and installed FreeBSd 5.0 the other day, and it seems that the installer is a little bit screwy - in particular, it failed to newfs my
/var slice, and as a result it wasn't mounted, and
/var was unpacked under the root.
I rebooted, manually newfs'd and moved /var from the root to it, but I'm guessing some permissions didn't come across properly, as X, and vi complained about access to /var/tmp.
Couldn't be bothered sorting it out, and went back to 4.7 for the time being...
Think I'll wait for 5.0.1 or 5.1 - some of the new features are very enticing (proper threads, devfs, etc), but for the time being, 4.7 works well enough for me :)