I am and have been since Jan 1 2009. I've lost 55 pounds on it so far. I was dismayed when alli took down their website right before the holidays and wiped out all of our discussions. We all had a ton of support there and now everyone has disappeared.
I use fitday to keep track of the percentages of fat, calories and protein needed to stay healthy. You must be careful that you don't overdo the carbs when you lower the fat. You should also maintain a low fat diet for at least a week before starting alli or you may be in for some unpleasantness.
The worst that I've ever had was just stomach cramps from gas. The threat of public humiliation is a wonderful deterrant! Good luck to you!