I would consider the HMC150 more of an "indy" camera. Professional cameras are quite pointless for people like us. In fact, the RED One is even considered an "indy" camera by most people.
Doesnt really matter, just thought I would point that out, haha.
As far as the differences go, its pretty much been pointed out here. If you really want to learn how to use a camera, I would recommend the 150 and buy books (barry green writes great ones) or dvds on how to use the camera and what everything means. Practice a lot with it and look at how each feature or option changes the shots. For instance, see the style of shot each gamma curve produces and find what you like best (plus read on what each one does). I dont believe the 40 has all of that.
Basically the 150 has a lot more options to customize each shot where the 40 is a more basic "auto" camera, and thats kidna what people mean by the difference of a prosumer (or consumer) camera vs a indy camera.
Great example is a GL2 or DVX is considered an indy camera where as an HV40 is consumer. Not because the GL2 and DVX (both SD) can create a better picture off of an auto shot, but because they can be customized where as the HV40 really cant be.
Hope that made sense and helped.