Skype and Windows Live Messenger are coming together. Update to Skype, sign in with your Messenger ID and your contact list and the IM feature will be there.
Right now Adium is open. It has 3 MSN accounts – one for podz, one is my live.com (Xbox Silver, not Gold) account and there is another. One IM client and multiple ID’s but Microsoft will kill them off. Like that’s going to get me to spend a single penny on their services. It’s just a loss no matter which way it’s spun.