Although it doesn't support a huge list of micro blogging/social networks but major ones such as Twitter and Faceboo, Identi.ca, Digg, FriendFeed etc RO Supported nonetheless.
*. Easy to use GUI with built in toolbar and icons, etc.
*. Search easily + supports saved searches.
*. Doesn't consume much of your GNU/Linux Laptop/PC hardware either.
*. It supports the D-bus protocol (a protocol used for communicating within application in GNU/Linux) thus other application can easily integrate it as a plugin.
*. Check for you spelling mistakes while typing.
*. Uses HTML for themes... easily customizable as well.
*. With the recent 2.3 update, now it has a multicolumn interface which enables viewing multiple feeds with ease.
These are few of its features mention, it comes with a lot more actually. Few days ago, a new update (daily build) is available through their PPA channel, if you use Ubuntu 11.04 Natty Narwhal (10.10 and 10.04), then you can install Gwibber by entering the below command in your Terminal.
sudo add-apt-repository ppa:gwibber-daily/ppa
sudo apt-get update
sudo apt-get install gwibber