The best way to find out how user friendly your site is, is to run usability tests.
This is a very big area, and for very high profiled webpages, is done in special created usability testing labs, that can track eye movement, while recording the session.
The test
###The test### ButBut you can make your own usability tests yourself, cheap and useful. More cheap tests is usually better than one expensive test. And you want to test your website before it's all done, so you can alter design and functionality that users don't understand early in the process. what's important to get a useful test, is to give your subject a task, and ask him or her to explain what they are thinking, and why they are doing what they are doing. You will sometimes be very surprised how people react in a way you didn't anticipate. Remember to take notes, if you don't record the test.
The subjects
###The subjects### ForFor most websites, ordinary people will be the best audience. If you make something that require a special knowledge, like a statistical analysis tool, you should try to hand pick the subjects. If you have trouble finding people, you can hire them to come in and test your website and pay them $20-50.