Identi.ca is quite handy as it has the ability to connect to Twitter and Facebook, and update your status there as/when you update your status on it. I am also using gwibber, a Linux/GNOME micro-blogging client which can connect to several social-network and micro-blogging sites, including all the above. The resulting flow of messages is best described here. I have also installed mobidentica, a light-weight Laconica/Identica client for Symbian S60, onto my Nokia E51, for on the go micro-blogging but I haven’t really used it in anger yet.
So basically, I can update my status on Twitter, Identi.ca and Facebook all in one place. E.g. from Gwibber, if I’m using my desktop; or via Identi.ca if I have access to a browser; or mobidentica via my phone. Identi.ca can also synchronise with services that use the Jabber IM protocol, like Google Talk and Nokia’s Ovi chat client.
The one downside is that there may be a bit of an impedance mismatch in audience between different micro-blogging/social-network sites. E.g. my Twitters/’dents tend to be more techy, which could seem strange to various Facebook family and friends who are not techies.. It’d be nice if Identi.ca had a fine-grained, in-line way to control which ‘dents were sent to Facebook.