I started this thread to let people know that some USB webcams do work with the Raspberry Pi, and in some cases may be a fit for your requirements. The camera board is a great product, and no doubt will get even better as the software matures, but based on your requirements, may or not be the best choice.

Camera Board Pros:

• Software utilizes RPi GPU, so for example encoding h.264 video has low impact on CPU usage.
• Excellent resolution (higher than most USB webcams) and excellent daytime image quality.
• You are supporting an open source hardware project, and potentially encouraging future improvements.

Camera Board Cons:

• Short, fragile, and inflexible ribbon cable. Camera board is best when camera will be mounted in the same box as the Raspberry Pi (or close by), ideally with everything but the lens internal to the box.
  No mounting hardware - you need to come up with something there (AdaFruit does sell a simple, fixed mounting bracket).

USB WebCam Board Pros:

• Most have some sort of ball-head type mounting, which allows you to re-position the camera as needed.
• Longer, flexible USB cable.
• Many are supported by Video4Linux, which lets you use it with nice software like Motion and GStreamer (Note: RPi Camera Board reportedly now has some Video4Linux support under development).

USB WebCam Board Cons:

• Typically slow, low frame rate video.
• CPU usage can be quite high.
• RPi does not have enough CPU horsepower to do higher frame rates, resolution, or advanced video compression. The Logitech C920 supports high frame rate hardware (in-camera) H.264 video encoding, but I experienced issues using this on the Raspberry Pi (may have been power related, though).