Anytime a USB port is involved charging will be limited to 500 milliamps. For example, a car charger for a cell phone will often charge noticeably faster than a USB cord will as it isn't limited to just 500 milliamps.

There are quick (~2 hours) chargers and super-quick (<30 min) chargers too for AA, AAA etc. I wouldn't use the super quick ones. If you use a quick charger, make sure it is a "smart" charger that will monitor the battery state and turn itself off once charging is finished.