I'm no expert, but since MR16 lamps are designed to be compatible with halogen lamps their internal circuitry, by design, has to work in concert with transformers and dimmers made for halogen lamps. This compatibility requirement has led to proprietary solutions which may have important side-effects.
I'm not sure whether the source can be considered reliable, but here's a couple of articles that worried me
http://ledsmagazine.com/features/9/6/8 and http://ledsmagazine.com/features/9/2/10.