I just spent about half an hour trying to figure out why my Ubuntu "alternate" 6.06.1 install was bombing out installing base packages. (I'm using the alternate install CD because I want RAID-1 filesystems from the get-go.)
I discovered instead of making the 1gb partition at the start of the disk /boot, I'd made it /. The 245gb partition was /home instead of /. (Just a simple desktop install, so I didn't want to partition it any more - people always bitch if /home runs out of space.)
I don't know what the best solution is for this, ie, if the installer can automatically detect if you've done something stupid with your / filesystem - obviously, Ubuntu's desktop install isn't going to fit in a partition that small, but it might if I had /usr and /bin and such on different filesystems. (An equally stupid layout, but you never know.)
Worth filing a bug report over? Dunno.