Fusion is a cydia tweak that will allow you to post to multiple social networks with one button. Fusion is the first part of the tweak, and allows you to use an activator setting to activate the social network menu. The second part of the tweak is a AssistantExtensions addon that allows you to use Siri to post to social networks, rather than typing the message in yourself. This tweak works with Twitter,Myspace,Foursquare, and Facebook.
Fusion can be bought on the Big Boss repository for $2.00. The tweak was developed by HomeSchoolDev.
Is this a tweak you would be interested in?