As a long time Gentoo user who is very new to Ubuntu, I thought I should offer some of my wisdom.
Gentoo is a great system, and it really is a great way to learn linux. You see everything from the ground up, so you learn a lot about how your system works inside and out. It's not newbie friendly...but that's more of an intimidation factor. If you're patient and you are willing to learn (a lot), then it is, in my opinion, the best way to learn about linux.
However...there are a lot of things that are quirky and less-refined from some people's perspective. I like to think that a lot of things are a series of hacks. For example, on my laptop, I have media keys at the top. To get them to work, there's a number of hacks that I could use, and it was some tinkering but I got them to work exactly the way I wanted. In contrast, Ubuntu seems to pick them up without question and they work out-of-the-box. The behavior isn't exactly what I want, in Ubuntu, but I havn't yet tried to tweak that -- so I don't know how easy that is to fix.
So of course the question is this: Why am I using Ubuntu now? Well, I use both. My laptop uses Ubuntu. There's a lot of odd hardware on there, and Ubuntu is best and picking that stuff up. Quite frankly, I don't really have time to be figuring out every detail and aspect of the laptop. Especially since I didn't build the laptop so I don't know the hardware as well. I also use the laptop for my field photography, so I like to have a lot of free space -- and the portage tree (the source files for updating your system) gets really large in Gentoo. But I use Gentoo on my desktop where resources are nearly unlimited, the hardware isn't anything special and I really want performance maxed out. Don't believe the naysayers...I can get a much faster system out of Gentoo than I can in Ubuntu...but it is at a cost of a lot of tinkering.
My advice to newcomers to Linux -- go with a simple setup like Ubuntu or SUSE. If you decide you like Linux a lot and you have "the bug" (commonly called an obsession), you'll end up in a distro like Gentoo or Slackware anyhow -- especially if you're a tweaker. You just can't beat the USE flag system that Gentoo has for tweaking.