Why is the EM5 so much more popular than the GH3?

Give it a chance!  I prefer the OM-D, but I think the advantages are evenly split, and most people will have a preference, with about half preferring the Panny and half the GH3.

There is one factor though - at the high end, many people know and love Oly, but Panasonic make compacts and fridges.  I have to say the panny branding has always been a turn off for me, and the Oly branding a positive, but I wouldn't choose a camera on that basis.

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www.flickr.com/photos/acam http://thegentlemansnapper.blogspot.com