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.