So the good news is that I tried to repair it and found a fix that works! I can't guarantee that it will work for you, but it did for me! Here is what I did:
1. Remove the battery.
2. Remove all 6 torx screws (T5) that secures the red internal frame to the display. One of the torx screw is covered with a black paper-like covering - don't miss that one. It's easy to push the torx wrench through the black paper material to get to the torx head.
3. Carefully pry the red internal housing from the display housing. Start on one side and work around the phone.
4. With the red internal housing removed, unscrew the small phillips screw in the upper corner to remove the motherboard from the display housing. The motherboard will now lift out of the display housing. Don't detach any cables.
6. As you remove the motherboard, look at where the power button is located in the display frame. Just under the power button - but attached to the underside of the motherboard - you will find the actual power button. It is a small silver square at the top of the motherboard with a black button at the top of the motherboard.
Now here is the fix that worked for me...
7. Flip the motherboard over and away from the display so the power button is facing up. There will be some cables holding the display and the motherboard together.
8. Get a can of Radio Shack Electronics Cleaner (contact cleaner). See attached picture of what I used.
9. Hold the phone unit so the power button is lower than the rest of the phone and spray the power button electronics with the contact cleaner using the contact cleaner with spray tube. I was careful not to overspray the mother board (but some did get on the motherboard), and I made sure I didn't get any on the display housing.
10. Let contact cleaner dry for a few minutes, reassemble, and test when completely dry.
That's it! The contact cleaner must have cleaned out whatever corrosion or material was in the power button because it works perfectly now. I did this on Monday of this week and still no problem three days later. Total repair: about $14!
If you are apprehensive about taking apart your phone, here is a link with step-by-step instructions: http://www.ifixit.com/Teardown/HTC-E...eardown/2979/1
So if you are experiencing the dreaded power button failure and you are out of warranty, give this a try before you throw your money away. Hopefully it will work for you!