I'm going to go ahead and recommend this creature without playing with it for more than 2 hours, because the feature I'm using now--which Omni calls "Focal Point" is just what I've been looking for. Focal Point draws a bright rectangle of light around the user interface object you're currently working in. If it's a form element--for example, the text box I'm typing in now--Focal Point brightly lights up that box. If it's a web browser window, then the whole window lights up. It's another example of the "Lightbox" effect that's become so popular with Ajax/DHTML web programming. Outside the bright area, the rest of the screen is dimmed... thus, the "Focal" aspect of the tool. I had previously used--and liked--a menubar widget called "Doodim", which did the same sort of thing, except it acted only on the front window, not on specific form fields within that window. But Doodim worked by a bit of Applescript wizardry that tended to be as distracting as it was useful. So far, Focal Point is just what the doctor ordered! These old eyes are growing a bit dim, and this really lights the screen up for me!
OmniDazzle has an undetermined release date, but the current beta will expire some time in July. Enjoy it while it's still free!