I heard that one of the two USB ports provides more power, decreasing the charging time.
Still, I forgot which one is the powerful one. I would be nice to give a hint that's easy to rememeber ;)
It is does matter, this is a MBP from Early 2011, not one of the new 2012 series which has a very powerful charging port.
Update! I checked using System Report (you need to restart it after you plug/unplug iPad as it does not refresh itself).
So far there is no difference on my MBP, it it provides is 500 mA which is quite low.
Current Available (mA): 500 Current Required (mA): 500 Extra Operating Current (mA): 1600