I was happily using the Adium IM client when one day it asked to update itself to which I agreed. After I updated it it refused to allow me to enter my password to log into my IM server.
It turns out that a bug was introduced which caused an incorrect authentication mechanism to be selected under some situations. This did not really bother me since I introduce bugs in my programs all of the time and I don't expect them to be perfect programmers.
The trouble came when I went to the adium website to downgrade. They don't offer downloads for old versions. I reported this as a bug but they decided that users should not be able to download old versions.
So I have started using pidgin and will switch to that on all of my machines since I cannot really do without IM for weeks at a time. I suppose I could've saved an old copy of adium but that seems like a hassle.