That nothing more than a guess! Nobody knows for sure.
Just look at it this way. If many of Googles search results start showing stars. Google *could* stop the star from displaying properly (and make their seach results look horrible), or they could make examples of those site and ban them.
Personally I think it's a total waste of time and a keyword opportunity. I don't want more clicks, I want more sales! Stars make a site look 'spammy'