I remember at sebring, this year or maybe last year audi had to change the brake discs, pads and it was mentioned that they never expect to have to change anything brake related so it wasnt made as easy as possible for the mechanics.
Also at this years le mans 24 hours one of the gt1 corvettes changed the right side calliper and disc, Here is the video
http://www.youtube.com/watch?v=AhgTFs3rh50
Also gt2 Ferrari F430
http://www.youtube.com/watch?v=qh_7z-CJkBA
And not strictly GT related but still shows you how fast it can be done
http://www.youtube.com/watch?v=ppffC...eature=related
You must remember that the brakes are stupidly hot so it really is a tough job for the mechanics.