Using this portlet, you can
- Update your status
- Get messages that are sent directly to you (e.g. @prabhatjha in my case)
- Get list of folks who you are following and get their latest status. List is sortable.
You can grab the code from http://anonsvn.jboss.org/repos/qa/prabhat/twitter-portlet/ But this portlet can very well run on other portal servers as well if you know what deployment descriptors you need to modify.