I made a ROS driver (tested on Indigo), which is available at https://github.com/whoenig/crazyflie_ros. It should be in the documentation index at ros.org within the next few days. There is a demo included for teleoperation with an Xbox360 controller and data visualization in rviz/rqt_plot. The flie can be reconfigured using the ROS parameter infrastructure. Additionally, there is auto-reconnect in case the connection drops.
There is a short list of other existing drivers and how the compare to my driver on the github page.
I did not test with multiple flie's yet (only own one so far), however the connection uri can be specified for every driver instance. I did preorder the Crazyflie 2.0 and plan to add ROS support (together with testing of multiple flie's) whenever it arrives. I hope this will make the crazyflie even more attractive for researchers.
Any feedback, either here or using the github issue tracker, is welcome!