Seesmic Desktop will be celebrating tonight. Not only has the client reached an incredibly impressive 3 million downloads (albeit no telling how many by one person), but it also becomes the first mainstream Twitter client to integrate lists, something you can rest assured Founder Loic Le Meur will be proud of.

Le Meur and his driven team of developers have made the latest release available to its Team Seesmic (people who sign up for early preview releases).

With this release, Seesmic has the two most essential Twitter list features; you can view your lists and lists you belong to in the sidebar AND you can also add people to lists immediately.

To try it out, you’ll need to become a member of TeamSeesmic and await an email with download instructions.

Le Meur is keen to point out this is a preview release, more features will be added soon.