There is an interesting read on Ian Murdock's Weblog: Can't we all just get along? It talks about the differences between Debian and Ubuntu, the latter being a derivative of the first. Although I can understand Ian's problem, I do not share his views.
He's correct in some respects, for example that Ubuntu's packages often don't work on Debian Sarge. But the question is, do we want them to? Debian Sarge is a very stable and secure platform, one we (as a company) prefer to use in a corporate environment. In fact, 45% of our deployments are Debian Woody and another 45% are Debian Sarge. (The rest are mostly different hardware routers and Cisco stuff.) I wouldn't want those Ubuntu packages working on Sarge! As much as I love Debian, I never thought of it as a desktop distribution. It's ideal for servers, because it's stable and has slow update cycles. You know, when people say they choose for Red Hat because they can upgrade often, that's just not logical. Servers we have are deployed and work without a glitch. They don't need to be upgraded regularly, just patched for security holes! Why in the world would we want to upgrade a firewall/router? Patch the holes and give me those updates, that's all I want. And that's what Debian gives me. Sarge is due to be released very soon and the next version of Debian, Sid, will probably not be released for at least two years. And that's the way I want it to be. Server protocols don't change all that often.
On the other hand, a desktop is a machine that needs to be upgraded often. And when I take the time to upgrade, I want it to show. Not just some new buttons, but a nicer interface, new programmes, more features, better spam-detection, et cetera, et cetera. That's what Ubuntu gives us. Fast release cycles that matter. Each six months we get improvements. Do we want those improvements on a server? Usually not. But when we do want them, it's easier to backport an Ubuntu package than to build one from scratch.
Just my two cents.