You can check the performance of a website with the help of some websites like www.Alexa.com.
These websites are very useful as they show estimated performance of some site. You can check how well is any website doing with the help of these sites.
Alexa.com can tell you the Global Ranking of any website in just seconds. It shows total page views per user and the time that a user spends on average.
So, these sites are showing a mirror image of any site that you are interested in.
Authors must be very interested in seeing these sites providing valuable info.