It was impossible for me in Gen4 as we eventually got an N-router, and I didn't have other friends with the game. Gen5 I just wasn't into at all, so I stopped playing after beating the games. Now that Gen6 has righted all of Gen5's wrongs and then some, I'm much more inclined to catch em all, though I haven't really started on that just yet, but I've already seen close to 500 of em.

Way back in the late 90's I had somehow managed to catch all 150 in Pokemon Red.. I was able to enjoy it for a few days, and then poof, gone. A dear friend of mine, who was immediately branded arch nemesis, shut off my Gameboy one afternoon while I was saving. And when the instructions tell you not to switch off the Gameboy while it's saving, please listen. Still really like the games but have never had the urge to catch them all again.