APRS is quite popular around here. This area has a very good network in place to support APRS operations.
The local information source is
http://www.nwaprs.info You can start there for some good information about APRS.
As for the D700 - I have one, and it's a great radio. Besides being a very capable dual band radio, the built in TNC and APRS functionality allows for a quick and easy APRS tracker.
This area also has a UHF 9600 baud APRS network, and the D700 is able to access that system as well. The UHF system works from Seattle to Mt. Vernon.
Brad N7JGX
Whidbey Island, WA