I have had insomnia problems for about 10 years now. Your body does get used to it after a while, but not in any good ways. The reality of the situation is, exercise is the best way to bring your body down to a level of relaxation, as in go jogging for 40mins, shower with really hot water, then kick back and relax with a bookm or something, and you will feel drowsy in no time. It's all about breaking the even keel of inactivity and sleep. You bring your heartrate up really high, keep it there, and then when you do relax your tension and alertness will drop to a lower state than when you are normally sitting at a computer. It allows your brain to differentiate between sleep time and inactivity time.
If that fails, which it does for a select few, then keep regular doctor visits, because insomnia can also be a symptom of some very nasty things having to do with your health. Mental, and Physical.
I had a doctor visit three weeks ago, and they started me on a treatment for two weeks to see how I reacted. I worked like a charm. For the next two weeks I'm off the treatment though, and then I go back for an evaluation. We'll see how it works!
But I do feel for you man.