I have three m4/3 cameras now and do have some thoughts, in some ways they are more personal then anything else. I have a G1, PEN, and GF1.
The G series have the advantage with faster AF but the EP-1 isn't as far behind as some have indicated - in low light the advantage has to go to the G series with the focus assist lamp feature - when the focus assist lamp is turned off the cameras are about equal in low light, in my experience.
When using legacy lenses and this is important the clear winner for focusing in my opinion are the G1/GH1 hands down. That said I don't have the EVF1 for the G1F so I can't comment on how useful it will be with manual focus lenses. The two button approach of the Pen is at best awkward, but do-able with practice, I say that because I have seen great shots with the PEN and legacy lenses.
All the complaining about the EP-1 user interface aside the Pen has some very usable features missing on the GF1/G1. If you are willing to dig into the E manual and learn the interface the camera can be rewarding. Yes, I agree the menus are not exactly simple or intuitive and do require some effort. Less of a problem for me because I use Olympus DSLRs. An example would be the ability to set AF to the AE/AF button and turn-off the half press/full press AF (Mode 3 on the PEN). Can't do that with the G cameras, at least not yet.
Lenses go to Panasonic. The Olympus lenses are capable but I prefer the Panasonic lenses. I find the E Kit Zoom awkward and the 17mm needed another F stop. F2.0 would have been better and better build quality might have been a more suitable choice - similar to the original Pen lenses.
I prefer the Olympus approach to the LCD for shooting in AF mode from various angles, ie; the hip, shoulder, etc. That said the better resolution of the GF1 is very usable but not better than the Pen when shooting on the fly just different.
There was some complaining on the net about accidentally changing setting on the PEN while holding it in your right hand, and that certainly is the case - that said the controls can be turned-off and the on screen LCD menu used to get to the settings when changes are needed. On the GF1 I have had a similar problem and haven't yet figured out how to turn the buttons off - if indeed the buttons can be turned off. I don't think there is an LCD Menu equivalent to the Pen.
As for OIS versus the Olympus in body stabilization - I do prefer the Pen because it supports shooting with legacy lenses, but again that is a personal preference and many will never put a manual focus lens on their m4/3 camera. As it relates to video - I have a real video camera which I never use...
Just MY thoughts and of course mileage will very. More me thinking out loud than anything else.
Best to all. Terry