I started waking up earlier because I realized I had a much better work day if I did something I enjoyed before working. I start work at 10am, but I wake up around 7:30, walk the dog for ~2 miles, then relax and play a game, lift, do some blogging, read Hackernews etc. It's made my work day far more productive, I will say that. I also have a little one on the way so starting to acclimate my body to waking up earlier is better done sooner rather than later.
I recall reading a while back an article that stated people had more productive and overall positive work days if they did something enjoyable before starting work. I work from home most of the time and so it became more important than ever for me to actually _use_ the time I wouldn't be spending commuting. I definitely recommend it to everyone, particularly those who don't have a commute to "wind up" and decompress from their work day!