Vern there's not really one measurement to determine the value of a website if you're thinking of something along the lines of an Alexa ranking.
I'd agree that getting a web statistics package would be best.
Google Analytics is free though there are some who would suggest letting Google see all that data isn't the best idea. There are other stats packages out there you can get as well.
if you want to know where your pages rank for certain queries you can use a tool like the
Search Engine Positioning Tool from Digital Point. There are other tools that will check where your pages rank as well.
Ranking doesn't equal success though.
I think your friends are using Alexa just because they don't realize what it's really measuring. There are still lots of people who think Alexa rank means something. It doesn't mean anything, but people still think it does.