I tired it a couple of years ago with a trail of Modo 201, thought it was quite good. I didnt go over fully as I felt that I could do pretty much what I could do in Modo in Maya within the trial time.
I would feel that if you wanted to give it go, if your well into hard surface modeling and you think that it would speed your work as well as give you better results then I would go for it.
In a way, use it as an extension, similar to how some (me included) use Zbrush, I dont go purely Z to make an organic I bounce between Maya and Z to make the models, using the tools in both.
Use it for its advantages, theres no need for a complete swap, just take what you need from it, you could model in Modo then port over to Maya.
Then again the downside is the actual cost of the product. But I would think that you would pick it up quite quickly timewise as though the packages are different the overall basics will be the same, afterall a polys a poly and a verts a vert!
Steve
"No pressure, no diamonds" Thomas Carlyle