Re: What would you improve?

[Tim] "1) I wish there was 100 percent support to MR for all geometry types in maya (that means subDs) "

there are, you can now use maya subD's without hierarchial edits in mental ray. And you could always render poly meshes as subD by going to Window->Render Editors->Mental Ray->Approximation Editor and adding a subdivision approximation node to a polygon mesh.

[Tim] "2) I would like to be able to create my own deformers in maya from geometry, For ex. have poly or nurbs object act like a sculpt deformer. "

You can now use arbitrary NURBS geometry as a sculpt deformer. Check out what's new in maya 5 and the release notes. Always read release notes when a new version of your software comes.

[Tim] "
3) fix the .iff so it can be more effeciently used in todays top compositors."

the iff format has the latent ability to support any amount of arbitrary information, alias just hasn't made it do it by default. Its a programming task, but I agree, alias should expand the support of the format instead of leaving it up to us to add common things like node Id.