Really? I think it looks great. I especially like that the "forum jump" feature is available everywhere on the site. It used to be a pain to move from a discussion board to the user control panel, but now it's a snap.
I have 1024x768 monitor and I think the new layout looks fine. The extra space means that I don't have to maximize my browser window to look at the site, so now I can have 2 windows open at the same time.
As far as the performance, wasn't it slow right after the last upgrade? I'm going to wait a week before I come to any conclusions about speed.