Right, well I'm in week 4 or 5 of Development now... so I guess I've been doing this around 4 months and a week. I've lost just over 5 1/2 stone so far, and the side effects to date have been:
1) A little bit of nausea in the first few weeks, but only in little waves.
2) Going to the loo a LOT, but also has slowed down considerably after the first few weeks.
3) Wind! From both directions, quite a bit... apparently this is quite a common one.
4) Loose skin - like Mini said, I think a lot of its bound to be genetics. I'm 21 and my skin's a state, to be honest. I will absolutely be considering a tummy tuck/body lift when I'm finished, if the NHS will do it. As a rule of thumb, if your skin was tight before, it should come back to being similarly tight after a few months of finishing.
I think that's about it. None of the negatives come close to the positives, though. Hope thats helpful!