<p>How do you test the usability of the user interfaces of your applications - be they web or desktop?  Do you just throw it all together and then tweak it based on user experience once the application is live?  Or do you pass it to a specific usability team for testing prior to release?</p>

<p>We are a small software house, but I am interested in the best practices of how to measure usability.</p>

<p>Any help appreciated.</p>

I frequently take any new interface I'm working on to one of our technical support people.  They've heard every complaint about interfaces that you could ever imagine, so if anyone is going to think up potential problems, they will.
Also, and I'm not kidding about this, I often take the least computer literate person I know (you're mother is often a good choice...but they have to have
used
a computer before, otherwise it's going to by pointless) and let them loose on the interface with no instruction.  If they can't figure out where things are intuitively, then your GUI likely needs work.  Remember,
Don't make them think!
(yes, I know this is for web design, but it applies)