I've owned a couple of department store bicycles in the past with caliper brakes and I set the brakes up properly so when I squeezed the brakes the bike stopped pretty quickly.
I test-rode a bicycle from a bike shop a couple of days ago which had disc brakes, and it was just so slow to stop the bike, it seemed like the brakes were so weak. I checked the brakes on the spot by standing next to the bike and squeezing the front brake and pushing the bike forward, and there was no slippage, and same with the rear wheel. So I think the brakes were set up correctly, they just seemed to have no stopping power.
I asked the clerk about it and he said they would need to be "bedded in". I couldn't understand what he was talking about, but is it normal? And why can't I get a bike that's ready to go from when I buy it. Do I just buy a bike with weak brakes and use it for a while and after a few days the brakes will work better after it grinds a groove in or something like he said? Or were the brakes not set up correctly?