How successful is Stack Overflow careers? How many pairs of employees and employers found their match via Stack Overflow Careers?
This is interesting for me as I am planning to use the service to find suitable developers.
We're not tracking this information, and to be honest, I'm not sure that you can.
The determination of whether the pairing between company and developer is a successful one is only ever made after both parties have left our site. In order to capture that information we would have to send out a follow up survey to our users, and I'm not sure how useful that would be. It would be somewhat intrusive and would yield incomplete data at best (as you'll never get a 100% response rate and the responses would probably skew towards the best and the worst results).
It's also very subjective data: not all people are meant to work for all companies. What may work for one person won't for someone else. There are so many factors that determine whether a match can be made and if it is, whether it is a successful one that I'm not sure how well a single number will express that.
In short, anecdotal evidence (like aforementioned success stories) is probably the best way to get a sense of how Careers performs (and then there is always our money back guarantee in case it doesn't end up working for you. It happens.)