I had recently done some work on one machine and wanted to install it on a second.

The work relied on a number of libraries that I had downloaded and compiled from source and at first I was thinking I would end up redoing that on the other machine.

Well this isn't so much a tip as a realization, just use rsync.

rsync -av -e ssh /usr/local/ user@host:/usr/local/

Done! (Note this assume same architecture etc, in my case both were Intel machines running OS X 10.5)