When I was going through the tags to check what I've been missing and adding the ones I find interesting to me, I realized that hovering over synonym tags like wp7, displays a blank dialogue like this one:
I know I can't follow or favorite the tag synonym itself, because it's not actually a real tag. But I'm expecting them to act the same as a "regular" tag, and allow me to favorite the "real" tag (for eg windows-phone-7 in case of wp7).