Well, there are some reviews on Pixalo and I'm sure now you've asked the question other members will respond with any relevant experience (I have a canon 70-200mm L f2.8 IS and it's the bee's articulatio genu)
I tend to look
at this site when I'm after some reviews, pinch of salt sometimes required, a few of these guys have very high expectations and do all sorts of funky tests to prove that one lens has .001% more Chromatic Abberation than another and then slag it off for being useless, despite the fact no one could ever tell in real life use. However most of them are real people who actually use their kit to take photos of things rather than just testing them all day.
I've heard good things about the Sigma EX 70-200 f2.8 but have never handled or used one.
cheers
Dan