Those of you who say that the first 3 days are the worst - I found the opposite. The first few days were actually relatively easy but the cravings just started to get worse and worse as each day went by, to the point where the cravings were with me every waking moment - I was just desperate for bedtime all day every day because I knew that would be the only respite I had.
I have previously given up in the past completely successfully and very easily but I substituted my nicotine addiction for food. I ate and ate and ate and never felt full, put on loads of weight and went back to smoking in order to lose the weight. But at no time during that time (apart from day 1) did I ever feel like smoking a cigarette!
My last attempt (see para 1) I was determined not to eat any thing more than normal as I didn't want to put on weight. I still put on 3kg in 3 weeks!
Anyway as we can see from all the postings in this thread, everybody is completely different and it works (or doesn't) for everyone in completely different ways.
Anyway I have just seen my doctor today and the subject of smoking came up and he advised me NOT to try to give up at the moment because I am just starting to be premenopausal (lovely jubbly) and he says that is absolutely not the time to be trying to give up smoking! I love my doctor!

(French doctors are great because they never lecture you about smoking unlike English ones).