I have been happily using Ubuntu since 6.06.
Every subsequent release has been more pleasurable to use than the last, although these days I stick to the .04 releases (they just seem more stable)

I like the design, I love Unity (it's how my desktop was set-up before unity)
I love the software centre.
I love the way you shove a CD in a PC and it just works (I know, not an Ubuntu thing, that's a gnu/Linux thing)
Generally, for my usage pattern (myth, web, email, media, attractive interface), it hits the mark.
I like the fact I can put it on other people's machines and they just get it.
Most Linux distros, in they're default install, are kinda embarrassing

Maybe my opinion would change if I used it for something harder, like Android development.