If you were to go to other boards, you could bet your bottom dollar that EVERY reply would be a big anti-smoking rant. It is refreshing to see people are actually addressing the question in a more informative way rather than knee-jerk abuse.
As for fat loss, I can certainly sympathise with how smoking keeps one in reasonable trim. Smoking did blunt my appetite an awful lot, and I'd often reach for a smoke instead of a snack. There is also the argument that smoking boosts the metabolism, but I can't vouch for that.
When I stopped smoking, I put on around 20 lbs of fat in three months. I found myself snacking like crazy (30 cigarettes a day is an awful lot of "idle time" to keep your hands and mouth occupied). I must admit that it made me hugely depressed.
But on the plus side, my energy came back in a major way. I bounced out of bed in the mornings and had full lung power; it was amazing to be able to run up the stairs without feeling out of breath. Then of course it was wonderful not to feel the "fear" any longer, having to replenish cigarettes on a daily basis.
I did finally get round to losing the weight again and getting in the best shape of my life, and I can honestly say that there is no way I could have done it if I was still smoking. The bottom line is that as a smoker, my heart would pound like crazy after running only a few hundred yards. But with the return of full lung capacity, I could do crazy amounts of cardio and calisthenics.
If you want to lose fat, drop the cigarettes, really. It is soooo much better and easier without them. Don't be scared about putting on weight -- you will only put on fat if you fail to watch your diet. To this extent, I would recommend you go on the Atkins Induction phase for a month or so (it will totally regulate how much you eat).