Comments in -- style are too hard to mention cause they do not stop the eye-flow as // vertical slashes do. Comments in /**/ style are too easy to enter from the right numeric keyboard, but style require shift + some keys in the middle of keyboard.

From phisiological point of view - putting the right hand to the right for comments tells the body "i'm putting a comment", but putting in some way tells the body - I still type-in the code part.

I do believe that c++ and c-styled comments are not big deal to add, but they are big deal in making haskell more rapid typing programming language.