This is what usability testing is all about: find out the Big Obvious Thingie you've put on your web site is apparently completely invisible to most of your users:

Man I've love to grab a few people and watch them go through our sites. This test was SIMPLE: 10 people, 5 tasks:
* Can you go to
* Can you view the permanent jobs?
* Can you search for a web design job?
* Can you navigate back to the homepage?
* Can you post a job?
Simple tasks even.

Looking at the thumbnail of the whole site, I wouldn't have considered clicking it either.

What's Big and Obvious on your site that users may be missing??