The iPad only charges at normal speed when it is connected to the wall charger it came with. The iPad charger supplies 10W(5V, 2A), where as the laptop USB slot only supply ~0.5A, so charging the iPad via laptop can be really slow.
iPod and iPhone charges are also slow in comparison.
This is a suggestion from Dontunderstandmyipad by the way!
from Somerset UK on my iPad using IPF app