I stopped in 2001. It was difficult, but I was motivated. Things that helped were replacing cigarettes with a different behaviour, and changing routines I'd developed around smoking wherever possible. Also, I did my best to avoid smokers (or really just avoided smokers who weren't willing to humour me by not smoking when I was about). I read a lot of medical literature about the potential benefits of giving up, and I had some helpful friends who were very supportive.
For ages I was terrified of being around other smokers in case I felt tempted and ended up back in the habit, but I'm over that now. When I was at Bona Ballroom in February, I was a bit drunk and I was standing outside with some smokers and had a puff of someone's cigarette -- first time in years. I didn't like it at all, and have had no inclination whatsoever to do it again since.