I recently completed a MendelMax 1.5.
I have a pretty long thread on the Trossen forum about it.
Here is my take:
JWatte said it best that these things are a hobby in itself.
I think for a 3d printer to work reliably, it needs to be a precision machine, and plastic structural supports as found in the RepRaps are not ideal.
The RepRap community is incredibly helpful, and the fact that many can print as well as they do given the RepRap constraint of self replicating machines, is a testament to the engineering of the community.
I am currently designing and building a RepStrap, which is very similar except that I will not use plastic for supports or really anything I don't have to.
I have identified about 5 key areas of possible faults with 3d printers, particularly the RepRap, and I believe my end solution will address most if not all if these and give me a very reliable printer.
These things require a lot of patience and love to print, and I'm not sure there are any real exceptions to that right now.
I completely agree with JWatte that the two premier commercial hobbyist 3d printers are the Type A and the MendelMax 2, as both have little to no plastic.
Ultimately I wanted a 3d printer to enhance my robotics construction capabilities, and instead have kind of a sidetrack hobby which has taken me away from Robitics for the time being, unless you consider a 3d printer a robot, which it kind of is.
I do think the strength is remarkable considering its plastic, and you can get very creative by applying pieces if metal in key areas to protect/strengthen as needed.
It's also very, very cool to design something in openscad or blender and print it out, and use it.