The coolest thing I ever saw in the wild, a guy I once worked with wanted to transfer a directory of files from my machine to his (and maybe show off a little.) This was long enough ago that I didn't know quite how to proceed (time before rsync, scp...? Nah...) so he asked if he could do it and I let him have the keyboard. He tar'd (with z) the dir, piped the output of tar to ssh, with a remote command to cat it out…
tar cf - /mnt/data2 | ssh user@10.0.0.10 "cat > /mnt/data1/file1/file_data2.tar"
... and if the directory is large, you can 'split' it into multiple files: tar cfp - /mnt/data1 | ssh user@10.0.0.10 "split - -b 1024m /mnt/data1/file1/file_data2.tar"
This is really no longer relevant because, of course, we all just use rsync ... but in the modern world, my favorite example of the unix philosophy is: mysqldump -u mysql db | ssh user@rsync.net "dd of=db_dump"