I've used Yahoo Messenger for over a year as an alternative to MSN with the benefit that I could still add and chat to MSN contacts (albeit without video and file-transfer capabilities).
Unfortunately though, even MSN chat capabilities have been broken for over a month and there is still no update from Yahoo. This slow pace of development (it's been beta for how long now...a year at least???) makes me feel like surrendering and getting an MSN passport again :(...but what alternative is there if you want to chat to MSN contacts??? The sad thing is, if Microsoft buys Yahoo, Yahoo chat will be the first to go!