It does take quite some time to fully charge it. A LOT of battery(ies) in there to juice up. But a full 24 hours does seem a bit long. I drained mine to 5% last night. Plugged it in and left it. Was 100% when I looked this morning around 8am.
Yes, I've learned, it charges way faster when plugged directly into the wall. I have mine plugged into a power strip with five slots in it. My iPhone is plugged into it too. Over night I can always get to 100% on both the iPad 3 and the iPhone. I'm usually charging the iPad 3 from 40, 50 or 60% though.
One night I didn't Plug my iPad 3 in like I usually do and when I got up in the morning it was at 63%. I plugged it directly into the wall and within an hour and 1/2 it got up to 100%.
Wall plug is the fastest way! Oh yeah, and use the original USB and plug that came with the iPad 3. If you use the iPhone plug, I don't think you'll get a fast charge and the plug will get hot. The iPad 3 uses a lot of power and the iPhone plug does not provide that power.