It still won't import IK animation - you'll need to bake it on export. With Mecanim it'll find and bind the bones of a (roughly) human skeleton and then let you perform IK on those in-game (although I think the IK might be a Pro-only thing? I've not played with Mecanim yet).
The only thing I noticed is that you can't use modifiers from max, something like stretch and push stuff. Looks cool on viewport but Unity can't understand them. There's still a tool/plugin to solve this, though. On the other hand, you can export helpers and also IK Animations, as long as you bake the animations to FK…