I spent a lot of time looking for this information but with no luck. I finally decided to bite the bullet and find out myself. So for anyone who wants to know how much electricity the unit is using here's the information I gathered and the method I used.
I had already installed the unit making it impractical to connect my meter in between the radio and the car hookups so I removed the battery cable and installed it there. To my surprise, my car was drawing 2.8 amps while not running but with the doors open. Most likely a result of internal lights and other systems which activate to keep the car from being stolen. One advantage of this method is the ability to capture all electricity consumed by the radio when the system is running regardless of power routing.
Baseline Amps Watts Description
Car Only 2.8 0
Startup 3.7 0.9 11.34 Fluctuated between .9 Amps and 1.8 Amps until the unit was ready
All Off 3.7 0.9 11.34 Radio and Screen turned off, No Route Planned
Radio-Ipod 4.2 1.4 17.64 Playing Audio from the Ipod
Radio-FM 4.5 1.7 21.42 Playing Audio from the Radio
Radio-DVD 4.6 1.8 22.68 Playing Audio from a DVD
DVD-Video 4.7 1.9 23.94 Playing Video from a DVD
It's safe to say the F90BT uses between 1 and 2 Amps regardless of what state it's in. To me this is a very reasonable amount for a "standby" mode where the unit screen is simply turned off when not in use. Since car batteries have around 50 Amp Hours there is very little chance of the car dying over dinner and even over night. However there may not be enough power left to start the car which is pretty important. I'll test it this weekend when I have access to a friend and some jumper cables.
Let me know if you spot something inaccurate about my results!