Uses an unofficial API so might break any any moment. Google has said they want to provide an official API for goo.gl, but not there yet.
This is tested and works for Pentadactyl (http://dactyl.sourceforge.net/pentadactyl/index). To use it just drop it into your ~/.pentadactyl/plugins/ directory.
- gg
Shorten the current url and yank to clipboard
- googl
Alias for gg
Let me know if things don't work for you.