When compiling the latest ZFS-on-FUSE checkout, GCC (Debian/sid, 4.4-20090329-1) barfs with:

cc1: warnings being treated as errors
lib/libzfs/libzfs_dataset.c: In function 'zfs_prop_get':
lib/libzfs/libzfs_dataset.c:2348: error: offset '3' outside bounds of constant string
lib/libzfs/libzfs_dataset.c:2355: error: offset '3' outside bounds of constant string
scons: *** [lib/libzfs/libzfs_dataset.o] Error 1
scons: building terminated because of errors.

As this is really a gcc bug, we'd have to wait for a real fix. But we're impatient and there are two workarounds here:
1) compile w/o optimizations (i.e. no -On options)
2) compile w/o the -Werror flag.
The latter is probably what you want here...