I just got a new in box Fuze v1, and immediately upgraded to Rockbox 3.12 and can report strange USB issues. It will connect and charge just fine, although sometimes it takes an unplug and re-plug into the USB port to get the drives to show up.
Also, when transfering files from XP to the Fuze, the connection will randomly disconnect every once in a while, no rhyme or reason. But, eventually after two or three tries, I can get a few GB of data transferred over. I have read that bugs were introduced, possibly in the Bootloader code between v. 3.7 and 3.8, but am very reluctant to downgrade my Rockbox version.
One question-- I am showing in Rockbox System settings that the USB connection is only 25 Mbit/sec. The transfers over the USB2 interface are very slow, around 2 MB/sec due to this. Why is the USB interface not detected at 480 mbits/sec which is the theoretical USB2 max? Shouldn't I be getting closer to 10 MB/sec?