Yeah, my power button got very unresponsive after a few weeks, and it was so totally annoying, trying to bring it out of sleep or reboot, that I called a warranty repair. Got the phone back after about 5 days. Make sure to keep your battery, battery cover, SD card, and SIM card.
If you have additional questions, US customers may contact HTC by calling 1-888-216-4736. Outside the US, users should refer to the HTC website for the appropriate phone number.