I just did this using a stock Hassbian install, on a Raspi 2 Model B. HOLY COW!!!
- The UI is A LOT faster than it was when using the SQLite database.
- The OS, HASS Server, and Postgres all combined use only about 70MB of RAM!!
My next step (after doing a dd of my SD card) is to create a RAM disk for /var. This will entail writing systemd modules to tar up /var on shutdown, and un-tar /var on startup. The purpose of this is to not burn up SD cards.