I just signed up for a new service called Ping.fm. It lets you post to many different social networking sites from one place.
The service is still in beta, but if anyone wants to signup send me a private message and I may be able to give you an invite code that works.
These are the current sites that Ping.fm supports:
To send a message that will be published on your different profiles you can precede the message with a symbol.
For example, if you have setup MySpace and Tumblr to accept blog post, you can send a blog post to both by writing your message in this format @b title^body.
Example: @b This is my blog title^This is where I write my blog post...
To send a status update (e.g., MySpace, Twitter, Facebook), precede your message with @s
Example: @s This is the text of the status update
To post a micro-blog post, use the format: @m message
I've only started using Ping.fm today, but it looks like a great tool to manage multiple profiles on different sites.
The only thing I'm not using it for is Twitter, because I think Twitter messages should be more personal.
EDIT: I may have the posting commands above wrong -- I'll post back here with an update after I double check.