The xtrabackup docs contain steps for how to stream your backup over the network to another host, which is fine if the end result you want is a tar/gzip type archive, however, in some cases you may want to just get the files to the other host unextracted in order to create a new slave DB.
In this case you just want to get that snapshot into the new host as easily as possible -- in many cases I don't have enough storage to first put it into a tar or tar.gz and then extract.
To work around that, here is a way you can stream your backup over the network straight onto disk on the other side, while avoiding the need for an archive file as a stepping stone in the process.
Note: My bash-fu is probably not as advanced as some, so perhaps there is a more elegant way to make this fly, but it seems to work just fine for me.
ssh root@target-host "cd /data/target-dir; nc -l 9210 | tar xvif - " & sleep 1; \
innobackupex-1.5.1 --stream=tar /datadir/path --user=root --password=XXXXX\
--slave-info | nc target-host 9210
Once you are done, remember you still need to --apply-log before the snapshot can be used.
Hopefully this will save someone else a few minutes.