Many USB video devices (like Webcams, etc.) do work via the UVC standard. There is of course a Linux driver available, however this is not part of the vanilla kernel yet due to problems with the Video4Linux implementation. Therefore it has to be compiled manually or is added afterwards as a patch by the distributions. Fedora 9 and the new Ubuntu 8.04 for example do include the driver with their kernels.
There is a standard for USB video devices and the corresponding driver will soon be merged into the kernel.
If this really happens than video devices on Linux will make a big step forward: first of all a huge set of devices will be supported out of the box. Second, the support can be expected – therefore application developers can rely on it and can develop applications incorporating such video devices. Third, the developers behind the driver finally get credit for their great work and can continue the development on a stable base and with a clear future. And last but not least, the distributions have one patch less to worry.
Besides this information GKH identifies two big problematic fields in the current Linux device driver world: WLAN and video devices. WLAN just became much more sane and easy due to the new stack, but Broadcom devices are still a problem due to lacking support from Broadcam. And while video graphic cards support is getting better due to published specifications (NVIDIA, you are the only one missing!) many devices like video cameras and similar are still a problem and not well supported yet.
It is good to see that the kernel device developers have a clear picture of which device drivers are missing. And btw., it is nice to see that these drivers are for average desktop devices for normal users. So in this regard the kernel developers have an eye on the desktop.