The company keeps tab on referrals and other traffic sources and using Google Analytics Intelligence Alerts to single out most valuable of the lot, the converting traffic.
In addition to Google Analytics, They also use traffic patterns and other information to stay on the top.
Best of the article is that they explain the techniques used in their method, follow the link to find out.
So where is the Valentine? yes just like Jeff Gills and Vinoj Vijeykumaar, I am sure Matt Cutts would have ordered these shoes instead of Heart shaped Pizza. ( I gave her a nice dinner and I got Chocolate)
JAPAC: Shoes of Prey Stay Alert to Positive Buzz Via Google Analytics Blog: Happy Valentine's Day Sphere: Related Content