I'm with most of these guys..

Go out and grab the front brake hard and tell me if the rear wheel lifts up. If it does, your brakes/tires are fine. If it doesn't I would make sure everything is setup 100% the best it can and try again.

If I am riding the brakes and need to stop faster, I will gradually release the rear and apply more force to the front. My goal is to keep the back almost locked up. When I am really stopping fast the rear is off the ground so I just let off the rear completely.

I would recommend practicing braking fast in dusty parking lots/etc. using only the rear, only the front, and both. Gives you practice controlling the bike in a skid/endo/etc. I ride as fast as I can almost everywhere I go (while still being reasonable) so I use my brakes often and hard but you always have to be prepared (what will you do if the rear wheel lifts, if you hit gravel, if your brake cable busts, etc. do you have an escape route if you can't stop such as a grassy hill, etc)