Hey guys come to the launch party for my new startup! 9pm Saturday, at the Mumblefrotz office: http://maps.google.com/united-states/california/san-francisc...
(Note: no actual party Saturday, and that's the example URL the post pointed to.)
In real world usage people will very often just cut and paste URLs directly into text, rather than figure out how to turn it into a link. Would you rather have this kind of link dumped in as plaintext, or would you rather have a lengthy machine-friendly link full of raw lat/long data, view choices, dbrefs, and whatnot?
Sure, fall back to a geolocation URL if it's not a point on a street grid. But I suspect that a huge percentage of the map URLs that people pass around are on street grids.
Then you probably live in the US. Most of the world is not so neatly gridded as the US.
URLs should first and foremost point to the resource (in this case a maps page) that you expect them to. This URL scheme cannot guarantee that, so it's a bad idea. It could work if you include a post code, but a post code is only marginally less ugly than a lat/long pair.