Ask YC News: Measuring Popularity / Awareness

A recent comment about TipIt ("feel sorry for these guys, going up against a well covered and now leader TipJoy") made me wonder (as tipjoy is brand new) how one would measure that.

What do you use to measure awareness of a service / market leader status? Compete rankings? Alexa rankings (flawed)? # references on Technorati? # of Google results for a company name / service name? Google Trends? ComScore? Quantcast?

This has implications for tracking the success of PR / Marketing efforts.