LaunchBar 5.1 just launched with a slew of new features, including automatic updates (finally!), maintaining your "Hide Dock Icon" preference across updates (finally!) and support for third-party event-creation utilities (e.g., Fantastical).
Another new feature is the ability to invoke--out of the box--an application's text-based service. For example, if you want to tweet with the Twitter app, you simply select the app from within LaunchBar, hit the space bar and bang out your tweet.
The hangup for me though is that you still are routed to the Twitter app (it just uses the system's Services functionality), where you finally can publish the tweet. It effectively is no different than selecting text in a document and choosing "Tweet" from the Services menu, or just using Twitter's "Global new tweet" shortcut, and actually is a bit slower than the latter.
If you want to tweet via LaunchBar, I think my solution still is the quickest, most elegant way to go about it.