| Here is what happened when I published "HN pickup ratio" web app on HN: - 10,000 visitors from 100 countries in 3 days (good sales pitch, isn't it?) - 95% of traffic comes from robots (for first few days, after that it goes down to 60%) - this is based on disproportion between number HTML and CSS serves (should I also count here the 405 error?) - 57% visitors are from U.S. (of that 30% were from California) - 58% visitors used chrome browser (IE is just 1%!!!) - 52% visitors used apple device (where 11% are mobile Apple devices) - 30% visitors used laptops (based on screen resolution 1440x900 and 1280x800) Here is the raw data (big png poster): http://hnpickup.appspot.com/hnpickup_web_app_statistics_snapshot.png | 
Though I'm a rare exception, my web browser is configured to ignore CSS completely, including both in-page styles and all additional loadable files. A configuration like this is very rare because it's difficult to do and the result often breaks sites. The only place where it is common is for people with visual impairments.
A well behaved bot will (typically) announce itself by its User-Agent string. A securely configured browser (IMO) will never send a User-Agent string or Referrer, and will reject cookies as well as ignore javascript --Needless to say, this breaks a whole lot of sites, but suffice to say, HN does have a higher percentage of people wearing tin-foil hats than the regular populace.