Recently, I did a 42-day voluntary abstention from drinking. And, unlike everyone else I know who has tried this, I didn't cheat. It was inspired by a 21-day abstention a few months prior, which was due to a backpacking trip on which we decided not to bring any booze.
At the end of these periods I felt great, physically and mentally. After starting up again, my alcohol consumption was less than it used to be. Sleep was better than ever, and I wake up feeling refreshed - the better sleep is far and above the most noticeable effect. Generally I just feel healthier.
The social thing is a challenge, but not impossible. I actually forced myself not to go out any less, I still kept every plan with friends to visit bars, clubs, etc. Just drank a club soda. I quoted the above because I had a similar experience: when you are sober, you quickly realize that there are a few or several of your friends who you cannot stand to be around sober. You realize how annoying they are.
It was fun pushing myself for three and then six weeks. It inspired me to follow up with a three-day water fast (that was particularly painful, again I did not cheat). I am interested if any HN readers have suggestions of other self-denial tasks to try out.