While my initial thought is that this is a clumsy idea (it means that you have to re-save your network password on all of your devices for the new SSID) I'm warming to it for a crucial reason:
Recently a couple of things have bothered me in WiFi geolocation:
1. I moved house. The location of the access point I own still registers the old address.
2. I bought a new access point secondhand. The location of that access point still registers as the original owner's address some 3000km away!
Now the _nomap solution won't fix either of these problems because both access points are already in the database. I am waiting patiently for Skyhook to trickle down the updates, if that's even the correct place (how do I update Google directly?).
But it can be used to great effect in another case: mobile wireless hotspots. Any mobile hotspot, be it a device, a laptop (such as a Mac or running Connectify), or a mobile phone has no inherent location, therefore I would love it if manufacturers (because we know no-one changes defaults) could append _nomap in their firmware to the default network name on such devices.
Then again, maybe all devices should do this to their default name upon factory reset, because it only takes being tracked once to get in the database and it's harder to get out once you're in (how often is Google really going to be sampling your network name in your neighbourhood anyway?) as in my above cases.
Of course none of this stops the nefarious among us, the information is out there anyway...