What does Ubuntu have that Debian hasn't, except better marketing?

[DanL]

Yeah, I got tired of doing the six month upgrade dance and switched to sidux for my main OS, though I wouldn't recommend that to most people unless they're confident in their package management abilities.

I still use Ubuntu for distributing packages (launchpad) and such.

[Melcar]

Sidux is pretty cool. Generally I don't like rolling release distros since I depend on lots of stuff that tends to break easily under those types of environments, but for a "pure" Linux machine like my laptop Sidux is very good. And since it's Debian I feel right at home.
As for Ubuntu, I use it as my main OS because it has the perfect balance of stability and bleeding edge. Yes, that edge dulls after the first couple of months, but the stability part more than makes up for it in my opinion when it comes to having a mostly hassle free working desktop.