It is sorely needed. It must be designed in a way which cannot be easily misused or tricked by those with malicious intent. Adding links to the user's hompage of other social network sites is great (and should be part of a larger profile page each user should have). Automated verification, where the user post's a specific message, which then is picked up by the verification engine is both non-intrusive and can be automated for less overall impact and delay.

But let's not go down any path where users must provide login information for those other sites or have to grant permissions to post content on their behalf. Not recommended for obvious reasons.