Is it possible to configure optical trackpad (trackball) to switch on the phone just like iPhone? I find the power button hard to press with one hand. Pressing an optical trackpad (trackball) would be much more convenient. Are there any hacks for this?
I think turning on from shutdown is not possible without messing with the hardware.  I have a nexus one which is basically the HTC desire and using cyanogen mod i've been able to use the trackball to wake from sleep etc.  You will need to root etc and probably will void your warranty whatsoever.

Try the following link for more info:

http://forum.xda-developers.com/showthread.php?t=690477

also google  cyanogen mod (i can only post one link at a time)