Just submitted my renewal online today, hoping it's just as fast as some of the others have reported! Their servers had been down when I first started yesterday, so it was very slow and would not go past the "upload photo" step.
This afternoon I tried again and could see an immediate difference, everything was much speedier, and the photo did upload, and I was able to complete the submission!
A note for those who are considering the online renewal, you will need a JPG copy of your new photo - directly from the camera, no scans of prints, and you have to follow all the same rules for composure, clothing, expression, etc. They provide the guidelines on the site. The automatic cropping feature worked fine for me as well.
MyTravelGov (state.gov)
Theron