The big response to the E-P1 means more m43 bodies in the pipeline. My guess is that we'll see a larger body from Olympus, and a smaller body from Panasonic. What remains to be seen is how soon the "big 3" (Canon, Nikon, and Sony) will respond to this format. One "regular Joe" friend of mine says he loves his Panasonic G1 Kit (He came from a Casio Exilim). He's still on the learning curve, but was able to take good pictures straight out of the box. If more people discover this type of easier, smaller interchangeable lens camera, Rebel and Dxx sales might start to suffer.
It seems like Olympus wants to develop higher-end m43 bodies as well as more affordable ones. That should go a long way towards appeasing non-photographers who think the E-P1 is too expensive or photographers who think it isn't serious enough (mainly due to the lack of an eye-level viewfinder). On one side, I'm seeing plenty of people walking around with superzooms or other non-pocketable non-interchangeable-lens cameras, so it seems like there are plenty of users willing to give up the pocketability of ultra-compacts. On the other side, many "enthusiasts" (including myself) are picking up the E-P1 as a supplement to their larger "main" systems. They're not willing to give up the depth-of-field control, high-ISO performance, accessories, and overall image quality of their current systems. However, if Oly and Panny play their cards right, m43 could become more than a second system for the hardcore gearheads.