The E-600: not really a new model from Olympus, but rather a very slight modification of the E-620, supposedly intended to bring the cost a bit down in order to make the camera more competitive in price.
While Olympus does not explicitly list the changes, the specs indicate that most of the changes (simplifications) are just in the firmware: omission of some (three?) "creative modes", of aspect ratio cropping, and of in-camera double exposure. Actually, I will not be missing any of these features, although I do not quite understand how would a removal of some tertiary-importance code from the firmware make a camera cheaper to make.
The only visible (and cost-saving) change is that the control buttons in the back are no longer illuminated. I know this is 70% cosmetics, but the illumination looked good, and it could be quite helpful under some circumstances. (Well, at least fewer things may go wrong now.)
Otherwise both cameras seem to be identical, so, with those minor exceptions, all I wrote about the E-620 applies to the new model as well. It remains unclear if both will be manufactured concurrently, but I don't expect this to happen.
This the second such non-event from Olympus this year, after the E-450. Perhaps the market would not buy a camera model more than six months old? Certainly, a disoriented consumer is a good consumer; at least many marketing people (Olympus or not) seem to think so. Are we going to see an E-610 in March, with one more "creative mode" added?