I think it's worth a bug, BUT I am not certain it's just the availability setting that has an impact on the battery. I think "location" is also having an effect, and more than I would expect. Sketching the scenarios:

• No availability. No network updates, so should be longest battery life.
• Availability set, but "My Location" set to "Do not Show". Only state changes are starting/stopping phone calls, so should only require keep-alives and very infrequent updates.
• Availabililty set, "My Location" set to "City level". Since this level of location should be findable by tower triangulation (the "a" of a-gps), this should be nearly the same energy as the point above + "has location changed" computing + a weekly fetch of the a-gps cell tower to location mapping tables.
• Availability on, "My Location" set to "District level". I would think cell triangulation would be detailed enough, so as point above + additional updates due bouncing locations due to changing tower attachments.
• Available on, "My Location" set to "Street level". This would require GPS satellite fix, and thus it would consume a lot of power.

Those scenarios are leaving aside movement and inconsistent 3G signal strength.

I say above that the My Location setting seems to be having more effect than I expect because even when I am set to "City Level" on location it appears to be powering up the GPS hardware. I am just judging this by the GPS icon -- does anyone have a way of checking directly if the GPS hardware is powered?