I have done a write up on performance concerns with USB webcams on the BBB. In the article you will find test results for the PS3Eye and Logitech C920, options to allow you to capture images above 320x240 at frame rates greater than 5 FPS, concerns about the amount of data transferred over USB, as well as C code for a program I used to grab the images. There is also a Python script to patch MJPEG frames that lack the Huffman table required to open them as jpegs. Hopefully it will be useful to those who are trying to use the BBB for CV applications. The article is at http://blog.lemoneerlabs.com/post/BBB-webcams
Feedback is appreciated.