There has been hundreads of upgrades done all over the package. I will try to list a as much as I can think of.
obviously everyone has heard about the Long hair feature. This can be used many more ways. you Can make any nurbs curve dynamic. eg. you can turn a spline IK in your character dynamic and it will give a great flow when being animated like a bees legs or an octapuss.
The soft modification tool is great. this will allow you pick any point on your poly mesh and pull scale and control falloff of the modification. There is also little widgets in the attribute editor that allow you control the taper of the falloff
char animation - huge update. basically trax was re done. UI is very easy to use and understand you can trim clips, cycle, scale hold and also you can lock clips mute and solo. you can crete clips from expressions and contraints. also import multiple audio tracks into trax. many more updates.
you can now retarget animation from on skeleton to another. trust me this is awesome. the two skeletons can be completely different and it will still work. Also label your joints in viewport
You can also now redirect your skeleton
in the hypergraph you can now move animation curves with a falloff or select multiple curves and apply a lattice to them. This is great with mocap data.
you can now apply deformers to particles and you can control falloff on lattice
the hypershade now has all the mental ray shaders integrated into it. you can create bins to organize your shaders. Also there is a text box to search for shaders and more stuff available here
PSD file integration. You can create PSD files in maya and also save out the UV snap shot into the PSD file. you can select which channels you want to map and this will create layer folders in the PSD file.
wow im getting tired already...
for MR rendering now... IPR is working. Fur, fluids now render. Countour integration in the mental ray globals. image based lighting and you can see the image in the viewport. Photon and final gathering visualization maps. Render blurry reflections and refractions. GLOW is working. and more
general texture stuff including DDS support and PNG formats. you can also bake normals on your poly mesh.
some modeling features are polygon mirror cut, vertex normal edit, PFX on polys also you can convert nurbs to polys as a single mesh.
Tones of updates to file referencing have been done. load and unload refrences in viewport. you can control which references will load when scene opens. automatically crete anotations and locators with references and many more
web panel in the viewport is now supported and you can actually have mel scripts in your html. full java support uses mozilla.
you can also crete multiple cloth caches and view and blend between them. see stress areas of your cloth also
sorry guys got to go very busy but trust me when I say this is a huge release for Maya. I only listed things that came to my head but there is so much more guys. TXS!
sorry for the spelling mistakes, I wrote this quickly and please if you guys have any questions ask away and I should be able to answer.