I have been using Differin for six months now and in my experience it has been brilliant. I was on Dan's regime for a year, and although it worked brilliantly, I wanted to see if I could find a product which didn't dictate the way I lived my life (having to use it religiously twice a day everyday, only using white bed sheets and towels because of the bleaching, not being able to work out or go swimming/in the sea because it would wash the product off, having constantly dry skin). So I asked my doctor what I could use, and he prescribed me differin and an antibiotic.
A lot of people will tell you how horrendous the initial breakout (IB) is, but I think it depends on how bad your skin is in the first place and the type of acne you have. My acne was not big red pustules, just a lot of under the skin bumps. So I had quite a lot to come to the surface (as differin increases cell turn over). But I found that by the end of the first month I noticed significant improvement, and now six months in I am clear. Please bear in mind that I did take antibiotics so these will also have helped.
I think if you have the patience to stick with this product than it is completely worth it, but if you want to find something that works quickly than this is not the product for you. But in my experience, very few products work quickly and effectively on acne. Also, I have found that the product made the top layers of my skin quite flimsy and they peel off easily...so if you pick your skin (as I often do) you end up taking more layers of skin off, which can cause large red marks. Just something to be aware of.