You haven't mentioned what your photographer friend shoots (subject). For a camera that is brilliant out in the field, the Oly pro DSLR's are hard to beat, especially coupled with their SHG optics. I never dust-spotted a singe image from 2003-2010 (over 500,000 images shot), with travels around the country and Europe including some very dusty race tracks.
We switched over to Canon in the fall of 2010, as I was doing the majority of in-studio work as well as needing the capabilities of tilt-shift lenses. Dust is a major issue on my 1Ds MkIII & 5D MkII, especially when shooting for catalog with smaller apertures on plain backgrounds.
Just remember, it's just a tool, and getting the right one for the job at hand is the priority, no matter the make! If I had the extra money, I would add an E-5 and a handful of lenses in a heartbeat for my travel and inclement weather work.