The Ubuntu CDs that I ordered arrived at last on Friday. I installed it at the weekend and, so far, it seems quite good.
The install was cruder than I had expected — did I hit an expert install without noticing, or does it really ask "human beings" which kernel they want? Technically I was impressed though: it picked up both other distributions installed and added them to grub, and even accepted me going behind the installer's back ane remounting the install CD in another drive when the first gave errors reading some files.
While still clearly Debian under the hood, I liked the default setup. sudo only to root is a good idea. The only thing I really had to change was to add a smarthost to the mail server setup.