The observation about the buying habits of a particular individual can be integrated with other behaviour patterns, which are found out through questions like:

Does the customer purchase only when an item is available at a certain price?
Is the customer more likely to purchase on a weekend or even during the week?
Does it need to be […]

Alexa Ranking and Google PageRank are probably the two most well known methods of measuring the importance and popularity of a website. There are others as well who have joined the fray, read - Yahoo Backlinks and SEOmozPageStrength, but Alexa Ranking and Google PageRank remain the most commonly accepted web metrics methods.