Huh? It means you can select faces, some vertices and some edges, and Maya will remember what was selected for each component type as you switch between them. Both Softimage and 3ds Max have this feature, usually called something like retain component selection, and I have wanted it for years.

This simple addition might just save your sanity, as you can now jump between component types and use a mix of tools without having to constantly re-select the same vertex or faces over and over again. The really great part is that it works with the convert component to selection, making it easy to grab face loops and then quickly convert and add to the existing vertex selection.

Animation Features
Animators that I know have been asking for and drooling over the Motionpath edit tools like what Digital Fish had the moment they saw them. They will have to be satisfied for now with the new Editable Motion Trail tool and the ability to have more direct control over animation right in the view port. I think it is a good start and is a giant improvement over the previously unusable motion trials, though I hope they remove the extra node that is still being added to the scene and improve the speed when drawing over longer frame ranges. I had to check out the hot keys, marking menus and read the help files, because there are many options and features that really expose the control over the animation that at first glance are not as obvious as I had expected.

HumanIK (HIK) has finally received much more love in the 2012 release, including a fancy, though a bit hard to look at, UI and is now properly animatable with better integration with the rest of Maya. They added keying groups, Autokey support and better support for animation layers and better animation loading from MotionBuilder. HumanIK in Maya 2012 has replaced the older FBIK tools and is now identical to the solver in MotionBuilder 2012, as it was also upgraded.

While this is a huge improvement, there are still some bugs in pinning on the rig where the pins will not lock 100% as they do in MotionBuilder, and we are still missing some of the more advanced motion editing tools that will keep me using MotionBuilder when I can.

Rigging Updates
Following up on last year's skinning and paint weights overhaul, not much has changed, but looking more closely there have been some under the hood fixes that will be worth it for me.

Maya has pushed Namespaces for importing and referencing but never provided any tools to manage them until now. The updated Namespace Editor is much better at letting an artist manage and utilize namespaces to keep the scene organized with new tree-view display and the ability to remove the namespace -- seemingly simple but a must when working with large files or between software.

Also significant for me are the fixes to the Hammer Weights tool. Previously, if you accidentally selected an entire poly shell for an object and ran it, Maya would hang and crash but not anymore. The Smooth Skin Weights tool had this same problem and it would also cause some weighting issues for game optimized rigs. Now in Maya 2012 it no longer crashes and there is an extra check box in settings for "Obey Max Influences" allowing this very helpful tool to be used for game rigs that require limited influences.