The '08 Trek Madone has a large diameter, wider bottom bracket shell that uses the same bearings as "external bearing" bottom brackets (Shimano Hollowtech II, Campy UT, etc.) but dispenses with the threaded-in cups and accepts the bearing cartridges directly into molded recesses in the shell itself. It's semi-proprietary as it uses the same bearings as the crank makers but doesn't need the bearing cups.