It seems like all developers seem to believe they are closer to releasing than is reality or at least I always tend to think I'm closer. If you ever need a reality check then just demo your application to a boss, a tester, a friend or business associate. Nothing brings a little light to the subject quite like having to explain your application to another person.
When you find yourself making excuses for problems, lack of completed functionality or functionality in general you will start to realize just how far you are from a completed product. It is way too easy to just brush over the pieces of the application that you haven't worked on for a while. How many times have we left functionality for later or had a design meeting shift our focus to another section of the application. Then as time goes by we minimize the missing functionality and start to think we're so close to launching the product. A good demo will quickly remind you of just how much work is left to knock out. Keep a list of the OH NO moments that occur during the demo just as a reminder of the missing functionality.
A quick way to try out usuability is to have the person follow along in the application. Try talking the person through the functionality in the system without them seeing what your are doing on your screen. You may find that they are clicking on a totally different component on the screen than what you believe. For example we have a calendar for navigation on the right hand side of the application and a scheduler (which now I realize looks a lot like a calendar to everyone else) on the bottom of a split screen. I was instructing our test subject (we'll call her Sally) to click on the calendar to navigate to today's work. Sally would click and report back that nothing was happening. This went on for several minutes and finally I gave up and started a webinar. When I demonstrated the screen to her it became obvious to her that she was clicking on the scheduler. However it also became obvious to me that she viewed the scheduler as a calendar. What was totally obvious to me was a design problem for the average user.
In conclusion what I learned was what I knew...that getting the code in front of people early and often is the best path to developing usuable, successful software. It's just too easy to neglect this principal because we're all too busy building the applications and we let the "less important" items slip.