I'm gonna start off by saying I'm not in any good shape at all, now that thats out of the way.
I did p90x for one day, I couldn't even fucking finish the entire first video, by the time I got to abripper x, I was like fuck this!!! Then I came to work the next day and my arms felt like rubber, I couldn't even lift them above my shoulders for jack shit for about a week and haven't done a full P90x since. But with the p90x videos, I do incorporate some of the workout routines/techniques when I do workout cause some of them are good, just keeping at the pace of the videos is impossible. You have to be already in decent shape to actually hang in p90x.
Now I just jog 30 minutes at least 5 days a week, and lift weights every other day. Staring your workout out can be a pain in the ass, but when you're in the middle of your workout, and especially after your done, you feel like a champ. And when your done lifting weights, all you gotta do is flex your arm and you feel like a B@W5
HOPEFULLY one day, all this weight lifting will pay off and I get rowdy ass juicer arms like Alex from Street Fighter 3