I absolutely love FriendFeed's GMail IM integration. It's how I consume most of my FriendFeed content as well as lots from my favorite folks on Twitter that I have piped into FF via the Imaginary Friends (now Rooms) feature.
So, if I miss a few hours and want to catch up on what is going on in the Valley or from the folks I follow (and left GMail open on my Macbook), I can just open up the "Chat with FF" message waiting on me in my GMail FriendFeed label and scan. Plus, I can go back and search topics or people I'm interested in after a few days.
Not completely practical for everyone, but I love the feature (and greatly miss the good old days when Twitter had the same IM integration with Track).