I have only one concern with this idea. it's got nothing to do with what I like or don't like (In fact I like it, but I believe that's a personal opinion. I'll never be able to anticipate everybody's taste and I believe there is much more than that in interface design). Most of the times my eyes go from message to message very fast and my fear is that this will interfer with the reading...sometimes I dont even look who's posting actually...
I don't know if this is because I am used to to reading it this way, or because there is some real potential issues here. I think you will always have some use for extra space so, as long as you are not trading too much for it, it's a good thing.
