The early M1s had some deficiencies these weren`t found until the first Gulf War when the M1 served alongside the M60A3. The lack of an "infantry phone" at the rear made it difficult for infantry/tank cooperation (the M60A3 had the phone) - this was corrected after the War.
There are references to T72s being able to damage or even knockout M1s but pretty rare! The tank is also vulnerable to RPG7 hits to the rear and top hull/turret.
If you check the Wikipedia entry for the Abrams, there is a pretty good damage assessment section: http://en.wikipedia.org/wiki/M1_Abrams