Apple will be shipping a new charger with the 4th-generation iPad which should help to charge the iPad’s humongous battery faster than before. When Apple announced the iPad 3, it featured a significantly larger battery used to power the retina display and the LTE radios. As a side effect, the new iPad also took noticeably longer to charge up. With the new new iPad (confused yet?), Apple’s beginning to ship a higher powered adapter which comes in at 12 watts, as opposed to the standard 10 watt charger Apple has been shipping since the iPad 1.
It obviously won’t be a huge bump, though it will certainly help with charge time. Regardless, physics still apply here, so expect the charging of an iPad to take longer than that of a device with a smaller battery.