TweetDeck has been my primary desktop Twitter client for a while now. While I'd played with Twhirl and a few others, TweetDeck has provided the best user experience to-date. As of today, that user experience has gotten even better. For those who haven't used it, TweetDeck is an Adobe Air based desktop client for Twitter, that provides a multi-column view allowing you to more easily identify @replies and DMs.
The new version of TweetDeck, available for download, has plenty of compelling new features.
At the top of that list (for me) is direct support for StockTwits. Now you can see your StockTwits feed in a TweetDeck panel as shown here. This follows a $500k investment in TweetDeck from a group of angels including StockTwits co-founded Howard Lindzon, among others.
TweetDeck also now has hashtag support - when you compose a tweet, a drop-down displays links to insert any of the last 10 hashtags you've used. This is great when tweeting a conference or event. It also automatically inserts the hashtag when you reply to a tweet containing a hashtag. While this won't provide full message threads, it's a step in that direction.
Another feature that I'll use frequently is the one-click "email tweet", so I can more easily share tweets with users who are not on Twitter. I hope mobile clients like Twitterfon add this, as I frequently view Tweets on my iPhone that I want to forward to myself for later review.
There are lots of other features including the ability to translate individual tweets on the fly,
Marshall Kirkpatrick has a full review over at Read/Write/Web but the best way to start is to download it and play with it. If you're still going to the Twitter web page, you'll find this is a game-changing app for Twitter.