I have tried alli for a while, just the medication, didn't follow any particular meal plan. The point is you REALLY have to stick to a VERY low-fat diet and then I think.. if you're going to eat that healthy anyway, I'm just not sure the pill has any added benefit except for putting things into your body you don't know the effect of. A few weeks after I had stopped alli, I got my blood and urine tested (just a routine test) and my doctor had me thinking I had hepatitis for weeks because of some liver enzyme that wasn't normal. I turned out perfectly healthy after all, but still I wouldn't trust what alli does to your liver.
If you eat too much fat, you get the scariest diarrhea you have ever seen, but I'm sure you've read about that particular side effect.
Personally, I think the main perk of alli is that it can serve as an incentive to stick to your diet. You know what's going to happen if you don't eat well. But I don't trust it and if you kan motivate yourself to do the diet WITHOUT the pills, I would definitely do it that way!