I've been veging on posting this for weeks, and today BoingBoing did it for me.

There are a bunch of sites popping up under the heading of location tagging services. There goal seems to be combining the physical and virtual worlds into one experience.

Simply put...you see something cool in the real world, you place a mark in that spot and write about it on the web. When someone else stumbles upon it, they go to site, or send a text message, or whatever, to find out what's so cool about that spot.

With Grafedia, the mark comes in the form of blue underlined letters
With Blockies, the mark is a Blockies sticker
And with YellowArrow (the site that started it all) a yellow arrow sticker marks the treasure.

The advertising implications are obvious (You find a mark in the middle of the Great Lawn, you send a text message and get one back that says...drink Sprite). Hopefully, it won't go down that road, as there could be some very cool ways to combine the physical and virtual spaces into a really unique experience.