Macfusion has been forked on GitHub by another developer and a pre-2.1 development build is available that operates under Mountain Lion with no issues yet that I've discovered; both SSHFS and FTPFS work with FUSE for OS X if the MacFUSE compatibility layer is installed.
If you're feeling adventurous, you can download the build or build it yourself from https://github.com/ElDeveloper/macfusion2.
Alternatively, the original Macfusion 2.0.4 can also be convinced to work again as a front end for SSH mounts and this works under ML, if you also install FUSE for OS X and SSHFS (also available from the same site), then modify it so that the
sshfs-static binary points to the one from SSHFS, by running the following commands in Terminal:
mv sshfs-static sshfs-static.orig
ln -s /usr/local/bin/sshfs sshfs-static
However, it's a bit finicky. Mounting and unmounting SSHFS filesystems works fine, but attempting to remove a filesystem from the Macfusion list will fail.
I am unaware of a way to re-enable FTPFS functionality in Macfusion 2.0.4.
More information: SSHFS Installation: Macfusion