TwitStat’s current top 10 list is below, showing ranking and % of users posting from each service today. Note that where users made use of multiple methods, all were counted. The list is constantly changing, and the Top 100 can be found here.
1 Web – 29.57%
2 TweetDeck – 10.58%
3 Twitterfeed – 5.54%
4 Twhirl – 4.92 %
5 Twitterrific – 3.79 %
6 Tweetie – 3.65%
7 Text – 3.40 %
8 Mobile web 3.00 %
9 TwitterFon – 2.96 %
10 TwitPic – 2.94 %

Seesmic which claims to be the Twitter for video has just acquired Twhirl. Although Seesmic is still in Alpha this seems to be a good purchase on the outside. Twhirl is one of the most popular Adobe AIR apps and allows users to post to their Twitter, Jaiku and Pownce accounts. This is the first acquisition ever of a pure AIR application and im sure it wont be the last.
For other coverage on this acquisition take a look at BlogHerald and Mashable. Im also interested to see what Arrington has to say about the acquisition, because he is an investor in Seesmic, however Mark Hendrickson did the review for Techcrunch of the story.