I was in search for a decent desktop application(in GNOME) for twitter and finally the search ends at http://pino-app.appspot.com. I haven't tried too much apps for twitter, but was not really happy with the firefox extensions available.
Pino is a simple, fast and easy to use twitter/identi.ca client with a nice user interface. It fits into the panel as a tray icon and notifies via the notification system whenever a new tweet pops up. Setting up an account is easy and you can also use the URL shortening(goo.gl, is.gd) service from Pino.
The source package is available for download from the above link and also available as RPM package for Fedora. If you are using Fedora 12, then just run the command "yum install pino". Pino is available as a default application in the upcoming Fedora 13 release. Check the announcement here : http://lists.fedoraproject.org/pipermail/announce/2010-April/002787.html
Visit the project website for more details and screenshots. Feel free to use and contribute to pino.