I've been using a CPAP for 7 years since being diagnosed with sleep apnea (one of the more severe cases), and it's made a huge difference in my life.
Although weight and fitness is strongly correlated as a contributing factor, at the time I was diagnosed, I was an avid cyclist and prior to that, competed at a fairly high level as a middle distance runner. I'm sure that I had sleep apnea long before I was ever diagnosed. It was my wife (fiancee at the time) and our group of friends who noticed the symptoms when we went on overnight trips to go camping, skiing, hiking, etc.
It did take time to adjust to sleeping with the CPAP, but it's made such an improvement, I can't sleep without it now. And although my machine is old and huge and not as quiet as it once was (I really do have to figure out how to get myself one of those small, travel-friendly ones), I bring it with me whenever I'm staying somewhere else overnight (hint -- always bring an extension cord!). My quality of sleep has improved, and with that, my ability to focus and concentrate throughout the day. I wish I was being treated for it when I was going to school -- although I got my degrees, I can only imagine how much more rewarding the experience would have been.
While I can't say that my length of sleep has increased, I can honestly say that it's infinitely easier to get up before dawn for those early starts on the lake!