UBUNTU.
Seriously. You need a little more advanced install knowledge than Yoper (but if you've survived Gentoo, you've got that). It's as responsive as Yoper and a lot of things work right out of the box, like Yoper, there's a special AMD64 kernel/liveCD. It installs essential stuff only, and comes with Firefox.
Once I got my sound card set up, Linux was actually useful.
I found its chief weaknesses were its lack of out-of-the-box Audigy 2 support and no guide on how to set up skins.
You can find a fairly helpful IRC channel by opening up XIRC and choosing the Ubuntu server.
My experience with Gentoo: Whee, I have a system compiled natively from my box! Well, it's not like I can do anything with the init files to speed things up; they've got logic paths a half-dozen if statements deep just to start the network. Let's install KDE! Oh crap, I'm out of disk space and I don't even have the base libs installed. I guess Abiword, Thunderbird, Firefox, Kaffeine, two kernel sources and fluxbox ate up my
5 GB of hard drive space.
Not to mention the
known bugs that are
not mentioned in the install guide, causing me to waste two hours figuring out that the linker failure was because I specified an option that depended on another option being compiled. (Of course meaning I had to recompile a crapload of packages, because no one bothered to add two sentences to the guide for people who try to get by on the absolute minimum of packages)

My experience with Yoper: Gee, this is fast! And the init scripts are clean! Support is pretty crappy...and my firewire ports got detected as eth0...but OK, I can live with plugging my speakers into the headphones port. Now let's install a GF6600GT.
Oh look. Now Yoper completely freezes when it starts the X server, and the new beta doesn't help at all, but
does remove the boot-from-CD option and clean init scripts. I can use the X server in software mode, but that turns my movies into a slideshow.