Reducing iOS Background Location Battery Usage
Yes, WWDC 2011 Session 312 "iOS Performance and Power Optimization with Instruments" covers this at about the 45 minute mark.
When you finish using the GPS it can remain active for up to 10 seconds, and active radios both wake the device and while active prevent the device from 'sleeping'.
You'll be able to see this using the 'Energy Diagnostics' template in Instruments.