Both the 3rd Gen iPad and the iPad 2 include the same size 10W USB Power adapter but the new iPad battery is 70% larger...so it will likely take 70% longer. So if the iPad 2 would charge from 0 to 100 in 4 hours, the new iPad would take 7 hours to charge at the same rate.
Sometimes I'll use my iPad's 10W charger for my iPhone to speed up charging if my battery is low. The 5W power adapter for the iPhone was probably optimized by Apple, and using something different may hinder battery life...but who cares if you have an AppleCare plan!
The battery life is amazing for the new iPad, just make sure that you plug in your iPad each night after heavy use to ensure a fully charged battery for the next day.