Hellforge has an article on Blizzard's reexamination of the skill trees in Diablo III, suggesting that skill trees are gone from the action/RPG sequel based on Twitter posts (thanks nin). A tweet from Friday says "We're implementing and will be testing a new system that changes how skills are acquired. That's all I'll say. :)" A tweet from yesterday follows up saying the trees are being "removed/changed," making it all sound up in the air: "With our tweet Friday about the skill trees being removed/changed, what approach do you think we might be taking?" Meanwhile, a new interview with Blizzard's Jay Wilson on Diablo Fans addresses this directly, saying trees have been replaced by "a purely skill-based system," though this still sounds subject to change:

About that, we've decided to remove the tree-type architecture and we are moving into a purely skill-based system. This new system is still in the development stages and if it does not work, we still have plenty of options to fall back on. Right now, we're just trying different things and getting a feel for the few ideas in regards to the skill system that we have going on right now. It differs from the World of Warcraft/Diablo II type hierarchical styles and is more of a skill pool/path than a tree per se.