On Conversations, i have the avatars of both people on the left, with my name in a different colour to the other person's. It's much more readable that way as the time and date stamp is on the right hand side.

This is for both Gtalk and Skype (the only ones I am using - waiting for MSN and Yahoo to end up in Extras before testing as I already have access to them on my Blackberry Bold).

If you must, personally I would prefer the text to stay in the middle, and the time/date stamp and avatar be on the other side for one of the people.

What would be more useful would be the possibility of inviting others to existing "conversations" like you can on MSN and Yahoo. And if that were to be implemented, I would exepcted a 3rd colour, 4th colour etc for that person, but what would happen with the speech bubbles? After all, you can only have 2 people to make it flow on screen.