Someone emailed a link to an xkcd cartoon (not THE cartoon), I followed it, ended up consuming them all that same day. Didn't realise geohashing actually existed when I first saw THE cartoon, but later looked around on the xkcd site and found links to it.
So since late November 2009 I've been watching my graticule for reachable spots, but haven't actually made it to any yet. The idea seems very romantic but when you've spent 10 minutes stuck in traffic on the North Circular trying to get to a spot outside Luton for no defensible reason it becomes a bit less so...
I do have a car sat nav which can be persuaded to display GPS coordinates, and a camera, so if I do ever make it I'll be moderately equipped.
I spend almost all my time in London West, United Kingdom. I work around 51.5,-0.08 (near London Bridge) and divide my non-working time between 51.4,-0.2 (Raynes Park) and 51.51,-0.26 (Acton) - I've rounded these numbers deliberately out of vague paranoia! That seems a pretty large triangle to me, but in graticule terms it's fairly tiny.
I'm a software developer (surprise!).
 Days I might have made it
12/9/09: Only 19 miles easy drive south from Raynes Park? Will try to persuade fiancee. BTW here's a tip - after following the link to the google maps location on London West, United Kingdom and asking for driving directions from home, you'll have a map where "point B" is the nearest point on a road to the geohash - but the exact point will have disappeared. However, if you then go back in the browser to the original link location, you'll see both.
 Alternative mission
They're all so far away! So I've invented a more achievable (and environmentally friendly!) version - you're allowed to change the first decimal digit of the latitude and longitude to whatever's most convenient. So today - 2009-12-11 - (51.4052062, -0.2253502) instead of (51.9052062, -0.8253502) looks very achievable for me (5 mins walk from home in the middle of Cannon Hill Common). I'll probably be there around 9pm.
Sigh - I didn't make it, got diverted by family affairs and didn't even get to Raynes Park on Friday. Nor did I check any points during the weekend. Today there's a modified point inside Richmond Park... (51.4375906, -0.267574) instead of (51.4375906,-0.5675740). Might try for that tonight if my car will start - walking in from Robin Hood Gate.
Replaced battery in car yesterday after 2 failed attempts to get to that one!! Today, 2009-12-16, the alternative target of (51.5047030, -0.0838178) [instead of (51.9047030, -0.1838178)] is a couple of mins walk from my work, so I will walk there (and come back with my Navman tomorrow to see how close I got! ().
OK it's actually on top of a long thin building occupied by Tower paintball, Southwark theatre and Britain At War museum. I wandered in to Tower Paintball on the pretense of having a look, since I figured that was right under the spot! Finally remembered Navman on 31/12 - it was about right, crap round here with the tall buildings.