Compression hacks?

For various workloads, compression could be a win on both disk space
and speed (see, e.g.,
http://blog.oskarsson.nu/2009/03/hadoop-feat-lzo-save-disk-space-and.html).
 I realize Postgresql doesn't have general table compression a la
InnoDB's row_format=compressed (there's TOAST for large values and
there's some old discussion on
http://wiki.postgresql.org/wiki/CompressedTables), but I thought I'd
ask: anybody tried to compress their PG data somehow?  E.g., any
positive experiences running PG on a compressed filesystem (and any
caveats)?  Anecdotal stories of the effects of app-level large-field
compression in analytical workloads (though I'd be curious about
transactional workloads as well)?  Thanks in advance.

--
Yang Zhang
http://yz.mit.edu/