I think the PowerBoost1000 is 1000mAh charge rate only. The current draw while is use from the battery can be 2A+ (assuming your battery can handle it) with a 2.5A peak draw limit.
One thing about the powerBoost is that it talks about 1000C, the C rating of a battery or charger is normally a multiplier of the battery capacity in amps i.e. for a 1000mAh battery (1Ah) a 1C rating would be 1amp. Talking about 1000C implies you can somehow get 1000 times the batter capacity in amps, which you can't. To avoid confusion I think this should be removed from the description and just say 1A charge, 2A cont discharge.