I know someone who got them all in Diamond and Pearl. I got over 400 in that game before I got burned out.
It's easier if you own the other GBA and DS games cause they transfer over so you don't have to recatch them or trade. Plus WiFi makes it easier cause there's a kind of ebay-ish system where you can look up trade offers or make your own, or just hop on any forum and ask for shit.
Black and White have this constant WiFi thing going on that's basically what the 3DS does, where it's constantly searching for other people, and you can make trades or battles right on the spot with random strangers. Course, it's only out in Japan so I can't try that yet
Most people don't catch them all and focus on battling, cause there's a whole metagame around that. The calculations get pretty ridiculous and some of the strategies are pretty out there. That's why each release is exciting; new Mons throw new wrenches in your lineup, and some get nerfed or powered up. For instance, Ditto (remember that guy?) went from being the guy no one ever used to being one that might potentially be banned cause he has a new ability in Black and White.