Barack Obama was a keen user of Twitter while campaigning
Online services operate in a free market, says Bill Thompson, but more could be done to make them truly free.
Twitter, despite the attention it receives around the place with its high-profile users like Stephen Fry, is not the only micro-blogging service out there.
I quite like Tumblr, and Stumbleupon does something useful, while BrightKite links notes and photos to your current location and is growing fast.
One service I never really tried seriously is Pownce, and now I'll never get the chance as the company has been bought by Six Apart and is going to be shut down.
It seems that Six Apart, the people who make the Movable Type blogging platform, are interested in the technical skills of the Pownce founders and development team but don't want to run their own service.
They may end up building some of the same functionality into Movable Type, of course, but the shutters come down on Pownce in a week or two.
This sort of behaviour is unusual but not unprecedented. Google bought the Jaiku messaging service in 2007 and have completely neglected it, and services, sites and tools close or change all the time.
Lively, Google's 3D chat environment, lasted only six months, while the social network provider Ning has just announced that it will no longer support customers who are running sexually explicit services and is closing its "Red Light Zone".
Many Pownce users are upset at the loss of a service they found valuable. Those who had paid for premium features are annoyed that they are apparently to be offered a free Movable Type blog for a year when they had signed up for a social network and file exchange service.
But these things happen in the free market, and while the exact nature of the compensation offered to paying customers may be of interest to regulators, nobody is going to suggest that the government intervene in the takeover, closing or restructuring of relatively minor social network sites.
If Facebook bought Twitter and shut it we might all complain very loudly, but neither our Minister for Digital Engagement Tom Watson nor Barack Obama, both heavy tweeters, would even attempt to stop it.
Despite my so...t leanings I find it hard to get too worked up about the problems facing those whose favourite sites, services or networks change beyond recognition, start charging or shut up shop.
Mostly this is because I recognise that if you play in the market then you have to accept the downsides too, something that many investors are coming to realise on a much larger scale.
But is also because the rate of change and the degree of innovation online is so rapid that, like a toddler who has had their favourite plaything snatched away, few users will recall what all the fuss was about once a shiny new social toy is waved in front of them.
However, there are things that we can all do which will both minimise the pain when a service goes offline and at the same time do more to ensure that developers and site owners show some social responsibility.
At a minimum we need to be able to get our data out of these sites and services, to export the photographs and videos and other things we have uploaded.
We also need to take our contributions, so that the photos I download have the tags, comments and notes still attached to them.
But I'd also like to be able to retain the "social graph" that is implicit in the service, the list of friends and contacts, the nature of the relationship, the messages sent and received and all the other details.
At the moment there are no obvious ways of doing this, and the chances are that anything extracted will just be a data dump requiring a lot of work to be useful, but that does not mean it can't be done.
Like many other people I find that my social life is shaped by my use of social network services, whether it's a Twitter-organised meeting with BBC Technology Correspondent Rory Cellan-Jones at the Regent Street Apple Store or organising my son's imminent birthday party.
Unlike Billy Bragg, who asked Bebo founder Michael Birch to give artists a share of the company's sale price on the grounds that it has grown wealthy on the back of the music it serves, I don't see the social networks as "digital sharecroppers", to use Nick Carr's evocative phrase.
But having my data locked up in Facebook and Flickr and Twitter and BrightKite creates an imbalance in the relationship, one that ends up distorting the free market in the interests of the service providers.
I am as locked in to Facebook as a mainframe computer user was locked into IBM in 1965, or a desktop computer user was locked in to Microsoft in 1995.
Offering true portability will make the market more efficient, by encouraging competition and enabling customers to move between suppliers even when the current service is not being shut down but is simply not meeting their needs.
This goes far beyond the sort of portability MySpace and others are currently offering, which is about sharing profiles, not exporting them.
Providers don't like export tools because they rely in part on the difficulty of moving to a new network or photo service to keep their customers with them.
But the rules of the marketplace cut both ways.
If we're going to let Six Apart buy Pownce and close it, and offer no barrier to Google's decision to close Lively, then we can also ask that they respect the other side of the bargain and give their users genuine choice.
And, when it comes to online activity, choice should mean data portability.