Last time I was on Identi.ca I noticed that most of the messages were being posted from Ping.fm. This means that people are effectively are broadcasting there but who is listening? Possibly no-one.
Tomorrow the Today Programme on Radio 4 is going to ask whether Twitter is replacing blogging. I know that because they Tweeted about it.
Twitter might not be the best service or the first but it certainly seems to have hit some critical mass where it is now crossing over into the mainstream and before long it seems likely that it will be synonymous with microblogging in the way that Flickr and online photos are.
I’m currently following Stephen Fry’s wildlife documentary making on Twitter and even John Cleese is on there. When you have that kind of penetration I think most of your rivals can run up the white flag and retreat to the niche areas where they excel.
Echo One 
I think it’s extremely unlikely that Twitter is going to be the only microblogging site forever and ever amen. That hasn’t ever happened with any other market sector on the Internet. Why would Twitter be that different?
There are about 2 million people on Twitter; there are about 1.4 billion people on the Internet. It’s probably fair to compare microblogging in 2008 to social networks in 2003. Who needed anything but Friendster back then? Why bother with upstarts like Facebook or MySpace, when *everyone* is already on Friendster?
I and other Identica users and developers want to make microblogging an open standard, with thousands or even millions of servers. By last count, there were a few hundred microblogging services out there. We’ve got a cross-site protocol developed for our software, and there are at least two other implementations. I expect more to come, and I expect the spread of our Open Source software to mean that others can help the spread.
Oh, also: yesterday about 1/3 of posts to Identi.ca came from ping.fm and similar services. There are a lot of people using Identi.ca natively.
I think MySpace is a good example of what I am talking about. It is now primarily occupied by unsigned musicians developing audiences and sharing their music.
Services like Identi.ca naturally appeal to open source and open standard fans. However I think that for a majority of people what matters is what service their family and friends are on.
Look at something like Orkut that is stuck with it current population and can’t seem to break out any further.
Do the Identi.ca posting stats get published anywhere?