I also had Chantix prescribed to me by a doctor who oddly enough couldn't tell me much more about it than "it helps reduce cravings" at that point I was pretty desperate to quit and so I threw down the 100 bucks/month for it. It was great for the first month or so, but somewhere into month 2 I started having terrible problems with insomnia. This coming from a girl who is generally out by 10pm on a friday, 9 on a weekday like clockwork regardless of where I'm at (yes, I've fallen asleep at late night movies in the theater!). I had never had problems falling asleep until I was on this drug. I was getting something like 3 hours of sleep a night, it was terrible for work preformance. I started cutting out the nightly pill, reducing my intake by half, and the problems persisted for a couple weeks, so I stopped taking it all together.
I started it back up a few months later, and based on advice from another forum, cut the pills in half and only took 1/2 in the morning. This worked pretty well, the pills lasted longer and there was no insomnia, and really helped through the that first "hell week" off cigs. After a couple weeks I would start craving the cigs again, willpower would work for a while and then BAM some life event would drive me back to smoking. Long story somewhat short, I gave up on it. Still have a month and a half worth of pills in my medicine cabinet, and an ecig that has really saved the day for me.
A good friend of mine also just quit taking the pills after he had the same serious insomnia problems after about a month of use...... The crazy dreams though, we both decided they were an entertaining side effect.....
Neither one of us had some of the crazy withdrawl symptoms I've heard reported. I admitedly weaned myself off of them by reducing my dosage, but my friend did not. Of course, neither one of us could handle it for the full 3 months, we both quit after about 2.