Well, I spent several hours this weekend trying to get sshfs-fuse to work with dropbear and sftp-server without success.
Maybe it's a problem on the host side (A backup server at work running DSL v3.4.11 with OpenSSH_3.6.1p2 Debian 1:3.6.1p2-9, SSH protocols 1.5/2.0, OpenSSL 0x0090702f)
Incidentally, I noticed there are two extensions in the repository (sshfs-fuse-2.2, and sshfs-fuse), so I tried them both.
Since the latter occupies a smaller footprint, I suppose mine can be removed.