How do you test the usability of your user interfaces

I like Paul Buchheit's answer on this from startup school. The short version of what he said listen to your users. Listen does not mean obey your users. Take in the data filter out all the bad advice and iteratively clean up the site. Lather, rinse, repeat.

If you are a small shop you probably don't have a team of QA or Usability people or whatever to go through the site. Your users are going to be the ones that actually use the site though. Their feedback can be invaluable.

If something is too hard for one of your users to use or too complex to understand why they should use it, then it might be the same way for 1000 other users. Find a simpler way of accomplishing the same thing.

Once you have gathered all of this feedback and have a list of things to do, do the simplest ones first. That way you have forward moving usability progress.

What I like to do is give someone an install package, ask them to perform a number of tasks related to how the application works, and watch.

Hardest part is to keep your mouth shut.