As I mentioned in a previous post today.
People who have sites with nice Toolbar PR, "tend" to like Toolbar PR.
People who have sites with nice Alexa rankings, "tend" to like Alexa.
IMHO, they are useful for making "rough" extimates when decision making. For example, you pursue a linking partner. The TB shows a PR of 0. The site is either new, not indexed, or is not very popular. That is important to know before I start checking their backlinks. It helps me in that respect.
I don't buy links based on PR. I think that is foolish. Traffic is a much better metric than a green bar.
So we have Alexa to help us make the choice. Once again, a very inacurate tool. But it helps us me cross names off a list, before I get more involved with a site.
I think we can agree that the tools we have are very off base. But that's what we have at this point in time, so love 'em or hate 'em, can you think of any other sites that give more reliable traffic estimates?