Hello, I've coded a GRUB<->FUSE bridge. Available in 'fuse' branch.
Since POSIX usage is quite different from internal GRUB usage the
resulting filesystem is non-POSIX compliant, slow and read-only. But it
may be useful if your OS doesn't support the fileystem or partition
scheme of the multi-boot OS you want to retrieve data from. Alpha
quality. Example of use:
phcoder@debian.bg45.phnet:~/compile$ ./grub-fuse -r 'loop0,msdos1,bsd1' 
~/diskimg/bsd.img ~/mnt2
phcoder@debian.bg45.phnet:~/compile$ ls ~/mnt2
ls: cannot access /home/phcoder/mnt2/sys: Operation not permitted
bin  boot  cdrom  compat  COPYRIGHT  dev  etc  lib  libexec  media  mnt 
proc  rescue  root  sbin  sys  tmp  usr  var
phcoder@debian.bg45.phnet:~/compile$ ls ~/mnt2 -l
ls: cannot access /home/phcoder/mnt2/sys: Operation not permitted
total 7
dr-xr-xr-x 0 root root    0 Sep  6  2009 bin
dr-xr-xr-x 0 root root    0 Sep 17  2009 boot
dr-xr-xr-x 0 root root    0 Sep 17  2009 cdrom
-r--r--r-- 0 root root  512 Sep 17  2009 compat
-r--r--r-- 0 root root 6202 Sep  6  2009 COPYRIGHT
dr-xr-xr-x 0 root root    0 Sep 17  2009 dev
dr-xr-xr-x 0 root root    0 Aug 18 18:07 etc
dr-xr-xr-x 0 root root    0 Sep  6  2009 lib
dr-xr-xr-x 0 root root    0 Sep  6  2009 libexec
dr-xr-xr-x 0 root root    0 Sep  6  2009 media
dr-xr-xr-x 0 root root    0 Sep  6  2009 mnt
dr-xr-xr-x 0 root root    0 Sep  6  2009 proc
dr-xr-xr-x 0 root root    0 Sep  6  2009 rescue
dr-xr-xr-x 0 root root    0 Sep  6  2009 root
dr-xr-xr-x 0 root root    0 Sep  6  2009 sbin
?????????? ? ?    ?       ?            ? sys
dr-xr-xr-x 0 root root    0 Aug 18 18:22 tmp
dr-xr-xr-x 0 root root    0 Sep 17  2009 usr

-- 
Regards
Vladimir 'φ-coder/phcoder' Serbinenko