I cannot really answer your questions but will jut add my two cents since I see no-one else yet has. I won only the E-P1 but have great experience with the Pentax DSLR system and film cameras.

I find responsiveness and auto-focus to be somewhat between a good point and shoot and an SLR. I expected nothing different and am happy. I honestly don't think that it makes sense to choose a camera model based on micro-fractions of a second difference in performance in this area. Because all of these tiny differences are negligible when it comes to the much larger differences between different camera systems. And in any case uncontrollable real-world factors when out taking a pictures render minute differences a moot point.

All the Olympus models have small live histogram viewable as you frame a shot, and a larger one on review. You can choose which screens you toggle between in each case, so you could set up the LCD to show only an undisturbed image or the image + histogram and quickly move between them when composing.

In any case, I was extremely surprised at how accurately the E-P1 meters. Stunning.

I can confirm that resulting JPGs are excellent. I shot with RAW + JPG and in no case could tell the difference on my monitor. Of course RAW will allow more latitude in post-processing. Since these files are not that much bigger than the largest JPG files, I stick with RAW.

I think there are significant reasons to choose Olympus over Panasonic. One is the aesthetics of the PEN -- obviously a personal choice but undeniable. The Olympus LCD is better in bright light though still a pain to use.

But the number one difference is the IBIS which instantly makes all lenses much more usable on my E-P1. I would not do without.

I've owned the Canon Digital Rebel XTi myself. You'll love the E-PL2.

As far as I know it, no pen has AF assist.

Not sure exactly what you mean, but E-P1 has a feature in MF or AF+MF, in which the center of the screen is automatically magnified when you rotate the focusing ring of a compatible lens.
Or you mean AF assist light?

I'm pretty sure he means the AF assist light, which would be correct, as none of them have it.

yes that's what I thought he meant and what I mean too

Thanks for your input guys.

I have a final question for you:

Will EXIF data be available when using the Panasonic 20mm 1.4 or the Leica Summilux 25mm F1.4 on an E-PL2 body?

Thanks,
J

yes!