For some reason HTC didnt give the Imagio a way to turn the screen off besides waiting for it to turn off by its self or hitting the lock softkey......and still waiting for it to turn off....my solution is a screen toggle cab. that i found somewhere on the web a while back for my crippled touch pro that I have made use of on the Imagio! its about 16kb and does not a thing but turn the screen off. No need to worry about ram usage.
steps: Install the cab and go to all settings/personal/buttons and just remap the media button on the right of the call button to screen toggle