There's a great review article on the matter on the Atherosclerosis Journal (the edition in press now), but it's unlikely you'll have (free) access, so I'll try to share a few of the most important points
- Long term nicotine consumption modulates body weight regulation, by inducing adaptive changes in some of the molecules molecules which regulate feeding patterns and energy metabolism.
- There is also a metabolic withdrawal syndrome which affects about 80% of smokers. The symptoms are the ones we are already aware about, so nothing new there. However, and this is the nasty part, accompanying those symptoms there is also an increase in waist to hip ratio and an increased percent body fat due to increased caloric intake and/or decreased resting metabolic rate.
So yes - in short, nicotine does fuck up your metabolic rate.
A bit of good news - from all the weight people usually put on, only about 30% they can blame on the metabolism. The remaining 70% are due to what else they eat now they don't have a cigarette to put in their mouth (as Cornellian already pointed out).