[codingthewheel]

Respectfully disagree - Compete and Alexa both depend on toolbars, and no techie in his right mind wants to install such a thing. Quantcast doesn't use a toolbar, but it's heavily biased towards Quantcast-aware publishers who place the QC script on their pages. Long story short: these sites are bad for measuring traffic, but especially bad for measuring tech / power user / early adopter traffic.

[rrhoover]

Compete and Quantcast (if not "Quantified") are not good measurements of actual traffic estimates but they can usually report trends somewhat accurately. However, you make a great point about the tech/early adopter crowd which are the primary users for Quora.