If you want to motivate people get all your rocks in a row, says columnist Bill Thompson.
This afternoon my son and I drove from Cambridge to Lode, a small village just north of the city. When we got there we made our way to the old watermill and I lobbed half a brick across a river while Max filmed me.
Earlier in the weekend my friend Matt Jones, co-founder of the social network site Dopplr, had made a significantly more strenuous expedition to Knowle Park in Hildenborough to leave a rock shaped like a flint axe-head in a field.
Matt and I weren't just randomly littering the countryside, but making our individual contributions to the "Britglyph", a project that will eventually be the most extensive work of public art ever seen in Britain, one that follows in the tradition of the White Horse of Uffington and the Cerne Abbas giant.
It is a geoglyph, a drawing on the ground created by arranging stones or cutting the turf, but this one is spread over the whole country instead of just a field.
The people behind it have made a drawing of a time-piece inspired by the chronometer made by John Harrison, the Lincolnshire joiner who solved the problem of how to determine longitude onboard ship, and overlaid it on a map of the UK so that it stretches from Aberdeen to Southampton.
Each dot marks a precise latitude and longitude where contributors are asked to place a pebble, stone or rock, depending on your enthusiasm and strength.
The photographs Matt and I uploaded to the Britglyph website created an online record of our quests and marked out two more dots in this nation-wide artwork, bringing the final piece nearer to completion.
Britglyph was created by the team behind moblog.net with support from Shozu, a company that makes it easy to access social media sites from your mobile phone and which therefore has a clear interest in getting more people to upload photos from their phones.
It is a fascinating example of what is possible when you work with the grain of the internet, building something around the things the network makes possible instead of coming up with an idea and then trying to make it work online.
Britglyph relies on mobile phones with cameras and network connectivity, online maps, GPS and of course the connected community who make the whole thing "real" by their actions.
And the artwork is unique because it only exists in that strange liminal space that we have created between the internet and the physical universe.
It occupies the zone where offline and online existence blur into one, the space where cultural explorers Proboscis located "Urban Tapestries", their experiment in tagging locations with messages that could be read on smartphones.
This is the territory in which analogue and digital existences collide like particles at CERN, creating strange and short-lived forms of experience rather than new sorts of matter, helping us to discover more about what is means to be human in the networked age.
It's the place where Facebook "friends" get to know each other, and it only exists when online and offline are equally important.
Although Britglyph presents itself as a moblogging project it is really about finding ways to use the internet to turn engagement into action, and I was drawn in despite myself.
I've got a mobile phone with a camera, but I'm not a regular mobile blogger, mostly because I like to look at my photos and consider which ones to upload rather than throw everything online and see what happens.
Yet I dragged my son across the fens today just so I could drop a stone in a location chosen almost at random to make a dot on an online drawing, taking part in a work of art that only exists in the most abstract sense.
I did so because of Britglyph's presence on Facebook and of course the microblogging tool Twitter, which kept me aware of what has been happening with the project and showed me who was adding their stones to the work.
That constant awareness, combined with a general interest in the space where technology, society and art intersect, meant that I was pushed to make the leap from online observation to real-world activity.
It's the sort of leap that politicians are constantly trying to provoke, and we saw how successful it can be earlier this year when Barack Obama's campaign managed to mobilise hundreds of thousands of US supporters to do more than click on an online petition, join a Facebook group or send money.
They got people come to rallies, download lists of potential voters and phone them up and even get out and offer practical help on election day, and they did so using the same methods as the Britglyph team, although on a larger scale and with a lot more at stake.
The same sort of nagging may work in other areas. Tom Watson, the Cabinet Office Minister for Digital Engagement, has been making really good use of Twitter and other social tools for a while now, engaging in a serious online debate about issues like the importance of computer games to the UK economy or ways government can enhance its work in the digital realm.
And he has done so by talking to people in the places they already go to on the net, instead of launching more and more unwieldy online consultations to be neglected by the online masses.
Tom, and Obama, manage to find a way to reach people in the places they already hang out, like community organisers going to local schools, churches and cafes, and Britglyph is doing the same.
I'm pleased to have been part of this massive work of art, and more pleased that an online activity managed to get me to Lode on a Sunday afternoon, even if the mill was closed to visitors.
Bill Thompson is an independent journalist and regular commentator on the BBC World Service programme Digital Planet.