Well again, it depends on your uses.
Out of camera jpegs from Olympus are far far superior to Panasonic, so much so that alot of us think Panasonic G series should only be operated in RAW mode.
IQ of the E-P1 (and E620, E450) and GF1 (G1, GH1) and the NiCannoSony entry level cameras are so equal that no human can tell the difference... If printed, the printers have much more difference and you have no way of telling what came from what.
The technical differences come in IS and AF systems...
If you plan on using legacy lenses (either Zuiko Digital or any of the manual lenses out there) then I would recommend E-P1 because of IBIS that makes a huge difference.
If you are only going for native lenses and are OK with shooting everything in raw and PP everything before use, then the GF1 would be the choice.
If you shoot anything that needs a fast AF and you can't/won't use the techniques used back in the old days, then get a Panasonic G series or a DSLR... And in the case of DSLR, get a good one, like D700, so you can justify the extra size with extra IQ.