Ahhh Digsby, what a wonderful program. In my opinion, every person that uses multi-social networking accounts should have this. With support for email (read only unfortunately), major social networking sites (twitter, facebook, and you CAN send tweets and facebooks1), and support for IM! Yahoo, MSN, and more supported by this guy:
The software is very easy to use, nothing complex of the sorts. I have not experienced any epic lag or bugs. The developers are very active with this program, and best of all its free.
To set up your accounts, all you have to do is click the "Preferance" button in "Tools". From there its self explanitory. This is probably the simplest all-in-one program I have seen. View the Digsby website for screenshot gallery, support, forum, and download.
There really isn't anything to be said about this program. I have only one con with it, and that is doesn't support email composing or full message. It only displays the title and first line for the emails.
I give this program 5 Borats out of 5.
1=I have no idea what facebook updates are called for short. Thats why we love twitter more :)