My surgeon cleared me from most weight lifting restrictions about 9-10 weeks post surgery, and I work out 4-5 days a week, doing cardio and core every time, and alternating light weight training (generally I'm pushing weights in the 50-75lbs range, depending on the exercise, with high repetitions) and body weight work (pull ups, dips, etc) on different days. This routine has been in effect since early January.
I was advised to be very careful with things like squats and dead lifts that put pressure on the sphincter area, but we'll be revisiting these on a follow up I have early next month.
Many others have reported this advice from Shen's office, but my surgeon basically told me to go for it, but stop doing anything that hurts behind normal soreness immediately. Don't push too hard, especially at first, your body has been through a serious trauma with these surgeries, and you need to be mindful of that. I can see how a willy-nilly undisciplined work out effort could be harmful, but being mindful of strengthening the core, the area most affected by the surgical work, should help protect you as you move towards upping your weight training.
All that said, all the exercise make me feel better, seems to improve pouch function and has me in the best shape I've been in since I played soccer my first year of college. If my surgeon told me to stop doing what I'm doing, I'd start looking for a second opinion right away. I don't think anyone's ever provided any data to support Shen's limits.