No they are not. However, don't expect to see them take over yet. In fact, as far as I know, no BTX boards are available yet. Secondly, Intel had to have a new formfactor to combat the heat of the Prescott core Pentium 4's. Third, AMD's Athlon64/FX/Opteron CPU's requirements of the RAM being close to the CPU cause an issue with the BTX standard.
Quite honestly, I'd not worry about it for at least another year, and probably more like two before I'd think it's time to jump over. Even at that point ATX won't being gone completely.