It could be any number of things. Like everyone said, they need to break in. This means slow, deliberate stopping where the pads and rotors "bed in." If you or the mechanic just hauled ass down a steep hill, that's not cutting it (and is actually worse).

Some questions:

• Are the rotors straight/true?
• Are the calipers positioned correctly?
• Are the cables/housing of good quality and routed smoothly?
• Which levers are you running?
• Are the BB7s the road or mtb version?

BB7s are good brakes that are easy to set up. Unfortunately, some folks just don't "get it," and you end up with poor performance.