http://mtgsalvation.com/scars-of-mirrodin-spoiler.html
So MTGSalvation has started up their spoiler for Scars and already it's pretty interesting. Between poison coming back and how dominant planeswalkers have been in standard, Proliferate could be a real scary keyword, especially if it gets put on some cute, cheapish instant or sorcery.
And from the new art that's been leaked it looks like there'll be new planeswalker cards for Elspeth and Venser(!!!) so that's definitely something I'm looking forward to seeing.