A very common question in many physics forums online is the issue of "mass" and "energy" being "the same thing" (whatever "same thing" means). Most of the time, such question comes from someone who did not quite have the breadth of knowledge of Special Relativity and Quantum mechanics. All he or she cared about was the infamous E=mc^2 equation, and that is that. Somehow, all the other properties of light (having energy, momentum, and spin) and the particles (having "rest" energy, kinetic energy, spin, possibly charge, and particle number conservation) are ignored.
This is a rather informative and entertaining paper that was recently published in Am. Journal of Physics. Titled "Does Nature Convert Mass into Energy", it partially addresses the validity of the idea of "energy conversion" when there is a change in mass.
I think it is interesting that in many cases, the confusion comes in on how we define the words we are using. For example, what exactly do we mean when something is "the same", or something is converted from one to another? While such phrases appears to be trivially obvious in ordinary conversation, it is not so when applied to physics, especially when the very nature of the property of the object is under consideration. This is what most people who are not familiar with physics do not realize when they ask such questions. The question itself can, in fact, be the source of the difficulty and confusion.
 R. Baierlein, Am. J. Phys. 75, 320 (2007).