The title says it all. The developers of Seesmic, quite possible the most versatile social media client, have decided that they will no longer support Blackberry. As of June 30, they will focus on what they call their "most popular platforms: Android, iOS and Windows Phone 7."
This isn't terribly surprising, as RIM has fallen way behind in the race for smartphone greatness. The market that was once overwhelmingly business-driven has gone the way of mass consumption, and Blackberry is not in a position to keep up. Despite their push to develop apps to attract more multi-media heavy users and their recent Bing integration, it looks to be too little too late.
If you are a social media user (aka, a living, breathing human being) and you have not tried Seesmic, you should definitely check it out.