I am still looking for the perfect desktop client for Twitter AND Facebook. There are many Twitter clients that offer full functionality and even additional functions like automatic URL shortening and uploading of pics to twitpic and other similar sites. However, I haven't found a Facebook client (even standalone ones) that completely removes the need to log into Facebook via a browser.
For the meantime, I'm using 2 programs: TweetDeck on the Mac and Digsby on Windows.
TweetDeck - this program runs on Adobe Air which is a kind of mini-OS. The advantage of Air is that applications run the same way on whatever platform. The downside is that programs running on Adobe Air usually use up more memory. TweetDeck offers columns for a variety of feeds. You can have columns for tweets, another one for direct messages, mentions and others. Here you can tweet back, retweet and others. For Facebook, there are columns for the main news feed, photos, videos, etc. You can "like" and comment on posts. Even if the main window is minimized, notifications appear onscreen for a few seconds when there are updates. You can tweet back, retweet, like, comment via these notifications during those few seconds.
I still am looking for additional features on the Facebook implementation: Friends cannot see that you're online and you don't get any notifications when others comment or "like" your posts or the posts you have commented on. The lack of the latter is really what turns me off because I still have to log into Facebook to check for new comments. It supports multiple Twitter accounts but only a single Facebook account. After about 3 hours of use, it's not uncommon to have memory usage reaching 200MB+!
A nice feature here is that if you are doing something else while chatting with your contacts, a small pop-up window appears on your chosen corner of the screen showing the most recent message and a space for you to reply. After replying the window disappears allowing you to continue whatever you were doing without switching windows. It also uses less memory than TweetDeck.
The only thing lacking is also the absence of notifications of new comments on your Facebook posts. This is a feature which I really think will be the deal breaker among the social networks clients because this is the only thing that brings me back to the website. Mac compatibility of Digsby is still upcoming so I'm still using TweetDeck on the Mac.
