I was a huge proponent of Trillian (and a paying customer) for quite some time. I used it to connect my AIM, ICQ, MSN, and Yahoo accounts.
At about the time I ditched ICQ, it seemed that Trillian was getting bigger and more bloated with features I didn't care about, and had frequent connection problems. And so I tried Digsby and loved it.
Then I believe I got a new computer, and for about a week I forgot to install Disgby. Turned out that nearly everyone I wanted to chat with was either on Facebook or SMS, and so I gave up on Digsby.
It's been well over a near now, and all I use are Facebook and SMS, and occasionally Skype. I can't think of a single person I've lost contact with because of that change.