I did it two years ago - it's a great course with nice scenery. It was quite well supported when I did it in 2005, River City Bikes does a fabulous job.
I recommend you start as early as possible. If you start running out of time, consider turning around at the 40 mile mark to have an 80 mile round trip. The last 10 miles of ascent are the steepest and they took me about 2 hours to climb. As a result of which I got swept from the course by the SAG wagon about halfway down the descent and I didn't get to finish.
I'm not fit enough for it this year, but it's worth it. Have a fabulous time!