Why can't we all just... get along?
Some people have to use Windows, either because their jobs require it, or because they don't feel confident enough to try something unfamiliar.
Some people prefer Macs. Their reasons are their own, but I can certainly understand their viewpoint.
Others choose to use GNU/Linux/BSD/Unix/Solaris/Whatever, and that's okay as well.
If someone's decided to give linux* a go, then it makes sense for them to cut their teeth on a distro which is simple to install and use, and for that I'd have no hesitation in recommending Ubuntu. It really does "just work" (by which I mean that it simply works, not that it barely works) and it's really very easy for novices to pick up and run with. It also acts as quite a good ambassador for the *nix fraternity, as the bells and whistles which it allows even a four-year-old box to show off can impress even the most ardent Win/Mac fan.
At the same time, there are other distros which are considerably "better" for other purposes; it's a big market, and every niche and corner seems to be covered pretty well. I expect that people who "learn" *nix through Ubuntu will be more confident trying other distros from the safety of their new comfort zone. My thirteen-year-old son, who only recently started using Ubuntu in anger, has since been experimenting with Solaris, Mandriva and... erm... some other whose name escapes me at present. (You'll have to forgive me; I fall into the first category I listed above; I'm forced to use Windows primarily, because of the nature of my work.) - Okay, he's unlikely to be using these other distros seriously (and he's mostly looking for other "cool" stuff) but the point is he's _looking_...
Hey, at the end of the day we're all geeks, aren't we? Shouldn't we be uniting against our common enemy or something?
Uh... Medja whores, eh? Bunch of cunts.
*'Cos GNU/Linux, while technically correct, is more of a handful to type. Sorry.