I'm going to take this crazy thing everywhere I go. Home, school, work, date with the fiancee... she's already expecting it actually (I told her all about it of course).
I'll most likely swap out what is in there every so often, but here's my plan:
When playing on the DS: put a happiness based evolution Pokémon (like Eevee or Chansey) in and strap it to my ceiling fan (if at home).
While out and moving: put any Pokémon from my active party in and level it up as I go about my business.
I am importing HearGold from Japan, and I already put in a pre-order for SoulSilver's US release, so I guess I'll wind up with two PokéWalkers come this spring. Then I can double up on the above plan. :D