In order to unlock all non-event routes, one would need to walk approximately 1000 miles (1609 km), assuming 2000 steps per mile, with the assumption that no watts are spent or received as gifts.
If walking with the Pokéwalker the recommended 10,000 steps per day, it would take 200 days to unlock all the routes, with the assumption that no watts are spent or received as gifts.
The Pokéwalker uses a CR 2032 3V watch battery. The average battery life for the pokewalker is 3 months.
Removing the battery will cause all steps taken and watts obtained to be cleared. The Pokémon inside will not be erased.
My question is, everytime you connect the DS and Pokewalker together does it record the steps and watts you've taken and store them somewhere? If not this could amount to a fail of epic proportions. If the average month is 30 days, the battery is expected to die with average use at about 90 days. If it takes 200 days at the recommended number of steps in a day, there is no way to actually unlock everything properly.