hi,
i did it last year and this year. It is fun, tho a lot of people. You have to get there early if you don't want to get stuck walking...we got to starting line up at 6:30 am - hardest thing is standing around til 8 am when ride starts - it's a bit chilly and there are long lines at dunkin donuts and bathrooms! but both years i got there at 6:30 and we were actually riding (on the bikes) by 8:15...a traffic jam going into central park (about half an hour of start and stop), but other than that we could ride pretty freely, tho you always have to be careful because there are so many people.

but it is a fun event, and ABSOLUTELY FLAT!!! (except for little teeny inclines on the bridges)....