I have been working on a lot of USB firmware lately and found the best forum for this was at the
USB Implementers Forum website. I found a lot of useful information and some great help from the community. Up to now, the
USB-IF forum message board was accessible with a free registration. Unexpectedly, the forum is now
closed to the public, my recent registration denied by the site. Yesterday, I noticed all links to the forum removed from the main USB.org site and all posts older than a few weeks deleted. I posted a message asking about the forum status but now, unless there is some mistake, I won't be able to see the response and assume it's members only.
I am seeing a lot more interest in USB for embedded systems designs, including USB devices, embedded hosts, and USB 3.0. Most developer don't need their own vendor ID, many semiconductor vendors will let you use one for free if you use their chips. For small companies or individual developers, the $4000 cost to become a member is very prohibitive.
UPDATE: A few links to public USB forums:
Jan Axelson's USB Forum
PIC
Microchip USB Forum
SparkFun PIC USB Development Forum
Linux
http://news.gmane.org/gmane.linux.usb.general