bucksnorts, do you have a new Settings->System->Power option? If so, you can disable the "Auto power saving" feature which blanks the screen.
I think 10.5 has totally screwed up screensavers. There's a long thread about how the light on the front that should go off when the screensaver starts comes back on for no reason. I have the opposite issue - my light never comes on no matter what. Roku updates since the dawn of time have always come with a slew of bugs. Some get fixed eventually, some not so much, but they never get fixed quickly.