well I put pokemon that evolve with happiness in my pokewalker because...it just makes since. walking raises their happiness. plus it also raises my happiness because it makes me exercise :) you know...jog in place and the like :)
...I haven't been using the pokewalker much though lately. I already have all the catchable ones (pre-national dex) and all of the routes, so I probably won't use it again until I get the national dex and can get routes again and pokemon and stuff...