Recently I started using Identi.ca (http://identi.ca/rwdubsreviews) after using Twitter exclusively for a couple of years. One feature that came in handy recently is groups. Using ! plus the name of the group sends a dent (think tweet) to all the members of said group. For instance, !linux, sends to all in the linux group. I had a linux question so sent a dent and with in a couple of minutes had four replies. If you are looking for a Twitter alternative check identi.ca out. I might add there are lots of Linux users on identi.ca. Here is a list of apps http://status.net/open-source/add-ons/apps broke down between clients.Identi.ca is a micro-blogging service based on the Free Software StatusNet tool.
If you register for an account, you can post small (140 chars or less) text notices about yourself, where you are, what you're doing, or practically anything you want. You can also subscribe to the notices of your friends, or other people you're interested in, and follow them on the Web or in an RSS feed
Here is a blog dedicated to Identi.ca: http://ohidentica.com/how-to-start-using-identica-fast/