FUSE, the userspace mount utility in Linux, is prepping itself for inclusion into the main Linux kernel. Hence the last upgrade to Fuse 2.2. This version was recently introduced into the Debian unstable branch, which made it onto my computer after the last apt-get dist-upgrade. However, I noticed that the combination with siefs, the Siemens filesystem driver, refused to work after the Fuse upgrade :
# fusermount /mnt/usb siefs /dev/ttyUSB0
fusermount: old style mounting not supported
which was very annoying, cause I couldn't download the pictures I took with my mobile camera any more. The solution was to upgrade to siefs 0.5, and to kernel 2.6.11. Mounting the device with fusermount still isn't possible, but the regular mount works like a charm :

# mount -t siefs /dev/ttyUSB0 /mnt/usb