I did two rounds of P90x and looking back it was great to get me started but definitely can lead to overtraining. Of course diet being 75-80% of the solution is what really makes people look like the folks on the infomercial.
After my second round I went on a linear strength program (SL 5x5) 2-3X/week and stuck with that for close to 7 months coupled with sprint sessions or other HIIT workouts and 80% Primal/Paleo eating. The results during that show much more than the 180 days of P90x but I did focus a lot more on nutrition. We just recently started CrossFit.
If you like the P90x format, go through and dump all the isolation exercises and make the workouts consist of the compound and body weight exercises. This will shorten them and allow better recovery -- more Primal IMO.
Another option would be to go on a Starting Stength type program coupled with spot-on nutrition and HIIT/sprint workouts. I would actually lean towards that and then go to the reduced P90x suggested above after you have made significant progress with a linear strength program.