Day 28 starts in a few hours. This is my second quit. I gave up for almost a year between September 2008 and 2009, and fell off the wagon through a good night out at a stressful time, and a careless acceptance of a smoke while very drunk.
Still having the odd bad day, the odd very good day, with most somewhere in the middle. What I would say from my limited experience, is that failed quits are not wasted. This is much less of a struggle than last time, I guess from knowing that, horrible as quitting is, it is actually possible, and that I know roughly what to expect. I have also learned that there is no such thing as one cigarette for me. One fag = 20 the next day. I have to smoke 20 a day, or not smoke. There is nothing in between.
The other thing I have done differently this time is continued to enjoy alcohol. I almost stopped drinking completely when I quit before, terrified that it would make the quit so much harder. The problem was, when I did have a beer, it made the cravings suddenly re-appear from nowhere because I still associated drinking with smoking. My guard was low because I hadn't craved for a while, and combined with the alcohol's tragic effect on reasoning, caused me to crack.
This time, I decided to start trying to break the link between drinking and smoking early on, and had a few beers in week 2. To my surprise, although it made me want to smoke, I was still in a mindset of fighting the cravings, so dealt with it much better. My breakthrough last night was enjoying a pint with a mate (a non smoker), and not wanting to smoke.
Of course, the evil weed hasn't given all its grief after four weeks, and has more tests in store for me, but this time I feel prepared thanks to the failed quit before.
I guess what I'm trying to say is if you fall off the wagon, all that energy and time you've invested is not wasted. You can invest at least a good chunk of it in the next quit, and set yourself in better shape as a result.
Hope this rambling is useful to someone