With a Quickcam Web and Karmic.
$ lsusb ... Bus 004 Device 002: ID 046d:0850 Logitech, Inc. QuickCam Web ...
$ hal-find-by-capability --capability video4linux.video_capture /org/freedesktop/Hal/devices/usb_device_46d_850_noserial_if0_video4linux
With a Quickcam Web and Karmic.
$ lsusb
...
Bus 004 Device 002: ID 046d:0850 Logitech, Inc. QuickCam Web
...
$ hal-find- by-capability --capability video4linux. video_capture p/Hal/devices/ usb_device_ 46d_850_ noserial_ if0_video4linux
/org/freedeskto