I'm going to tile my upstairs bathrooms. Can I use EasyMat on top of the subfloor before tileing, or is Wonderboard or something like that necessary?

EasyMat claims to be as good as 1/4" wonderboard but easier to install. I use Ditra, Hardiebacker or Wonderboard. If you try EasyMat and it works for you please let us know, you'll be the first.