Profiles in Mozilla Firefox are really cool. I never used to see the point of them, but now I have loads and they help me to keep focused on a certain type of work or project e.g. dev work. I have one profile which simply loads webmin for my server. And my main one for just browsing, which has the most extensions installed.
Other software I'm loving recently includes liferea (rock steady), rhythmbox (now that gstreamer is maturing, it just plays everything and does shuffle etc etc) and gaim (of course! It's always been a favourite.)
/Updated 11th October/