The post didn't say just exactly how list support would be rolled out, or if you could export the groups you had already created into these new lists, but it is easy enough to assume they are working on it. In fact, the post says, "we're not just planning any old run-of-the mill integration...oh no. We think you'll find that what we have planned for Lists is going to take your social media experience with TweetDeck to new heights."
So if you are a TweetDeck user, worried about making more groups or starting your own lists, it sounds like Iain and team have you covered.
Update: Shortly after this was posted, Loic LeMeur of Seesmic said that his desktop program would also be soon supporting lists, in a tweet, saying: "OF COURSE Seesmic will have user lists very soon. I have them on my Seesmic Desktop already testing."