Gourmet Navigator

Hi all, I would like to introduce you my favorite site which uses a kind of viral-marketing, Gourmet Navigator.
http://www.gnavi.co.jp/
http://www.gnavi.co.jp/en/
This is a very useful restaurant guide, but English version is not so useful… I always search bars in this site; many of Japanese people are so shy that we can talk with our bosses honestly only when we are drinking....
Anyway, when I find a good restaurant, I can easily inform all members about the restaurant by e-mail which includes the name of "Gourmet Navigator". So, I always introduce all members about "Gourmet Navigator" unconsciously, and they may introduce other people by using this site, it will continue again and again.
Now, there are many similar sites in Japan, so they are struggling how to differentiate from others: provide coupons, launch various campaigns, etc. But they are almost same from the view point of feature and business style.
When the creative viral-marketing appears, someone imitates its idea immediately. Therefore, I think how to prevent imitation, how to keep originality, and how to differentiate from others are important.