I'm using it catch some pokemon that I havn't caught in the games yet. I'm currently putting my togepi in it. So far all I've gotten is a revive, an oran berry, and a kangaskhan though... so nothing too exciting yet.
I just got SoulSilver and caught a Sentret. Transfered the Sentret to my Pokewalker and ran the treadmill for 15 minutes which was about 3.5k steps and got 1 level . I like the pokewalker, it's good exercise haha.