I logged 10 trips the week of December 7 to December 11. Each trip averaged around 3.75 miles and ranged between 18 and 24 minutes.

For perspective - since I became a citibike member in May 2013 I have 630 trips covering just over 200 hours total time, covering they estimate 1525 miles.

Their mileage estimate is based on an average speed of 7.456 mph. That's a little slow. Using gps my trips average 9 to 11 mph depending on the number of stops for traffic and the like.