Hi Michael ...

My top five would include:

Dimensioning, text and line weight control (so I could use MoI as a drafting tool as well as a modeling tool) ... I guess that's 3
Printing from within MoI
Extrude is beautiful ... sometimes I would like to reverse extrude a face instead of having to trim with boolean difference.

MoI is wonderful for modeling ... I use it more and more for illustrating structures to clients ... it might be nice to be able to print to 3d pdf but that has already been discussed.

cheers,
eric