Yep, I have quite some experience with both. They're both great Here's a list of the differences that are really relevant for me:
*Compiling stuff on gentoo. You don't have to do it, especially not for the really big packages, but I don't know if everything works fine if you go binary only. With somewhat recent hardware (I have an Athlon 1800 with 512 RAM) it's not that much of a deal, so I guess you could be ok with that as well. One can also let the computer run over night when there's a bit more to compile
*Configuring things. Gentoo usually doesn't help much, you have to do it yourself. That's the idea, and I like that. Debian helps you more through configuring things (and does pretty well with that). The solutions in detail are very nice and slick in both.
*Package management. Since you mentioned it, Debian's apt still is king of the hill. Portage from gentoo is pretty nice, but it still lacks some desirable capabilities. But that doesn't hurt too much. Automatic updating is a one-liner for both and works just fine (of course, takes longer in gentoo, see above)
*Forums. I can't really tell you about Debian here, but it's very popular and you should find enough help on the web. Anyway, just wanted to mention that the gentoo forums are crowded with skilled people who'll help you out.
*Up-to-dateness. This is where gentoo shines, you can really have the most up to date software, because the package management is somewhat ports like. You can even mix some unstable software with a stable system very easily, which occasionally saved my ass. You can do that with Debian as well, but still software will eventually be a bit outdated (or more), and in my experience, mixing stable and unstable parts often results in broken things.
So, for me it's gentoo on my desktop, having the most recent software is just too cool I'd have Debian on my servers, occasionally something breaks in gentoo, but never in Debian stable.
One thing I can't tell you is about laptops, dunno if you'd be better of with another distro or so...
Hope that helps, cheers
Philipp