I don't like the buttons/icons on the slate skin but it's not bad otherwise. Having the avatar block on the right might be nice for reading on the Z (since I won't care if it isn't visible; i.e. hanging off the side).
I'm kinda torn to be honest.
I'll take the third choice!
PS: The IPB skin seems to force the page to be wider than the browser window when composing a post. That's annoying.
PPS: There seems to be a problem with a floating ad pane (i.e. the banner ad from the top of the page). When I press the little icon that jumps to the first unread post in a thread the floating ad appears in the middle of the page and blocks my view of the messages. It seems like the code that's positioning the ad assumes that the page is always at the top when it is first displayed (it's not a problem when the page initially appears at the top). I can fix the problem by scrolling the page to the top and then scrolling back down to the unread posts. This may only happen with the IPB skin (haven't tried it with slate yet).
Update (floating ad problem): I just tested with slate skin and it didn't happen. But then I switch back to IPB and it still didn't happen! So, I'm not sure how to reproduce the problem. It happened to me several times while reading new posts this morning though.