I live in Ashburn, Virginia (39, -77), and attend as many geohash points as I can, mostly falling within the District of Columbia graticules. My amateur radio callsign is N1TCP, and I will be listening on the designated frequency (146.520 MHz) on my way to and at geohashes.
I've reached/attempted a few points, although I'm fairly spontaneous (and likewise traveling light) - so I can't claim any of the Achievements with proof yet.
 Points Reached/Attempted
2009-08-23 38 -77 - Parking lot in the middle of DC, unfortunately fenced off for some kind of construction. (Washington, D.C.)
2009-03-12 38 -75 - Attempted while staying near Fenwick Island, DE. Point at the edge of the Great Cypress Swamp. Drove as far as the shoddily paved road. (Selbyville, DE)
2009-03-07 38 -77 - Point was in the middle of a horse field; almost reached. Odd Reston suburb for people with horses, it seemed. (Reston, VA)
2009-03-06 38 -77 - Interesting drive around an industrial park. Didn't quite make it because I didn't write down the coordinates. (Sterling, VA)
2009-02-24 38 -77 - Attempted a Midnight Geohash - stopped by a private road at about 4 minutes past midnight. Lots of deer about. (Zulla, VA)
2008-07-12 38 -77 - Reached. (Woodbridge, VA)
IRC: nwatson on Freenode/Foonetic