Since this feature is pretty new I had to bring myself up-to-date on how to exactly use the mount option. Since this is FUSE (Filesystem in Userspace) you don't need to be root to mount the actual backup. Still, it took my a while until I figured out the right parameters to make it all work.
This is how to make it happen (tested on Ubuntu / Mint / Debian):
sudo usermod -a -G fuse <your-user-name>
To mount the this backup repository, do a
obnam mount --repository /media/ds212/backup/<your-hostname>/backup_1310/ --client-name <your-hostname> --viewmode=multiple / --to=/home/<your-user-name>/tmp/obnam
Now you should be able to access your backup within
The cool thing is: With the option --viewmode=multiple just supplied above you can access all backup generations so far created at once. The latest folder contains a link to the, well, latest backup made.
To unmount the backup you need to be root however: sudo umount obnam
Have fun with this cool feature!