This may sound a bit controversial, but here it goes anyway.
I have owned 4 DSLRs and the E-P1, since I made the shift to digital photography in late 2004. I shoot RAW exclusively and post process using Photoshop. I print most of my "good" pictures using an Epson 3800.
In my opinion, it is impossible, by looking at the prints, to tell with which camera each photo was shot. Differences in exposure or post-processing are much more apparent.
I am as satisfied by the picture quality I am obtaining from my E-P1 as I am from my Canons. Whether I use one or the other depends on the requirements of the shoot, the appropriate lenses for what is being shot, and the need to use flash. Having said that, since I bought the E-P1, I have taken at least 20 shots with the E-P1 for each shot taken with either of my Canons.
For the record, I have a 50D and a T1i and good Canon glass. It may be the case that if I had a 5D Mk II or a 1Ds my opinion would be different.
FWIW, I have never been enamoured of the JPEG output of the Canons. I have seen straight from camera JPEGs here from Oly Pens that are wonderful, so it is possible that in a JPEG to JPEG comparison the Oly may have the Canon beat. Since I never shoot JPEG, it makes no difference to me.
Just my two cents.
Regards,
Antonio