Ubuntu is Debian run by pragmatic individuals.
My main complaint with Debian is that the people who run it care more about ideology than building a working Linux distro. Since Debian is Linux-by-committee, updates come at a snail's pace.
Debian has one great thing going for it: apt. Apt is probably the best package management system available for Linux, nice enough that I've bolted it on to my RHEL and SuSE machines. Debian also tends to be better-supported for non-apt software installs than SuSE, which is certainly a point in its favor.
The people running Ubuntu have essentially forked from a Debian base. They keep apt. They use GNOME. This is a distro with its shit together. Mostly.
It still uses Debian's text-based installer. Not a problem for me, personally, but it's highly off-putting for a newbie.
My first experience with Ubuntu (on the previous release, called IIRC "Hoary Hedgehog") was on some REALLY vanilla hardware - XP2500s on SiS 748-based boards, Radeon 7000s, RTL8139A NICs. Either I completely missed an option someplace, or de-selected something I should have, 'cause when I set it up, it didn't install X. At all. On about five machines.
I don't know what the hell the deal with that was, but it was not a positive impression. I've since seen it running on other hardware, and been rather more impressed with it. I've been torrenting it for a couple hours, I see I have a couple to go. I'll probably give it another go sometime soon, since I have a Linux class starting up next week, anyway.