I like white spaces too. But left sidebar is menu, ok. right sidebar tells me I can use hang out. left half of main content is the stream which is what I want. right half of main content tells me I need to complete my profile, suggested communities, trending. That's as important as the info stream?
The real issue is how to display a time sequenced (or other sequenced) info stream with a wide screen. Ironically the iPad / magazine boxed type view maybe the answer, but that's partly because the iPad screen is narrower, and it is designed for horizontal pagination. The facebook profile view is sorta like that but I don't like that either, because sometimes the time sequence gets confused, at least for me :-)