One of the reasons why I started training again is because I recently acquired a pokéwalker. It was also the reason why I was so interested in getting myself a copy of HeartGold/SoulSilver way before I managed to get a job.
The step counting function was okay, but I was somewhat disappointed when I found out that the pokémon you take for a stroll can gain only one level per data transfer. Still, I managed to catch a bunch of uncommon pokémon a lot earlier than in the actual game. The dowsing feature was also very nifty.
Since I switched to Pidgey as my party's flyer, I take along Hoothoot for strolls.
So far, I've been able to walk about 140,000 steps with the pokéwalker.