I am currently preparing a lecture and demos for a modeling and rendering workshop with Maya and Metal Ray for Bowling Green State University. I learned both before graduate school and used them during my studies till I found Blender and Yafray.
Coming back to Maya and Mental Ray is a blast. MR has so many functions it is mind blowing as I can understand them better today. But the dark side is OMG it is such a complex system to work with.
Blenders UI was often criticized in the past and I found myself that Cycles node network does not have as many options as MR however on the other side building a network is much faster with less clicks.
Maya has a similar interactive renderer as well and can use GI by using Finale Gathering and there I realized how
much faster and simpler Cycles approach actually is to evaluate a scene or design or material.
I think for high end animation Maya well is just it, but for my area of product modeling and rendering it is just overkill
and Cycles morphed into that what I only need and making scene set up lighting and material design a breeze.
Also having to deal with specularity and separate reflection values made me again appreciate the new material type Cycles is following.
Great job devs!