I currently use Ping.fm to post to multiple social networks at once, but it's been irritating me for a while and I'm thinking of writing a tool to replace it for myself. But I figure it's possible that someone has already done that. To be a suitable replacement it needs to handle twitter, and facebook; myspace, linkedin, and google buzz are a bonus, of course everything else is frosting. In addition to allowing me to send messages it must also be able to read multiple rss feeds and aggregate them to the networks I set up. If 2 or more tools, in conjunction can be made to do this that is also acceptable, e.g.
feedreader | cleanupforstream | post2stream.
If it doesn't exist I think I'll just write some Perl to do it for me, and put it on CPAN.