This is my first build. I had a laptop for a few years before this build, and I was never satisfied with it for gaming. I built this May 2012, and it is still going strong. I use it mainly for gaming, along with programming and other work. Lately I have been playing a lot of CSGO, along with some BF3, MW3 and Need for Speed (I pretty much play FPSes exclusively) and Halo 3 occasionally. I was fortunate to not have to deal with any DOA parts or RMA processes during the build.
Mechanical keyboards are probably my favorite peripheral addition. I rotate between the CM Quickfire Rapid with blues and a 6GV2 with blacks, with a small preference towards blacks. Blues are a little light for me, and I like the linear switches a little more for gaming. Both are great keyboards, and I would definitely encourage anyone who is thinking about a mechanical keyboard to get one. They are worth every penny.
I don't plan on upgrading anything until later this year sometime. Right now, my plans are to get the Asus VG248QE 144hz monitor and a new video card, but I'll just have to wait and see what happens.