RDS works in the US, but it depends if you have any radio stations in your area that are broadcasting an RDS signal.
It'll only work if you tell it to do an RDS search. Then, you'll end up with the added FM screen of FMType. This is where the RDS stations it found in your area are sorted into general categories (talk, rock, jazz, country, etc.). What info you get from a particular station depends on what the station does. Some only list their call letters or nickname with the station number (101.9 = B101, 89.7 = WGBH for Boston MA area). Some stations will put the current song title in the place of the call letters. Some will send an optional message (only viewable below 5mph), which could be another station ID, the current song/artist, the upcoming song/artist, or some advertisement, whatever the individual station wants.
What does not work on the 2004 Prius is the ASL and DSP functions.
http://www.vfaq.net/FAQ-misc.html#manualerr