How does the Olympus EP-2 compare to the EP-3 and the OM-D EM5?
Can you frame the question around your priorities? In general, OMD E-M5 is an all around better camera than the E-P2 and E-P3. The question left unanswered is it enough to justify the cost to YOU.
You can always use the money instead on some nicer lenses for your Nikon..... Depending on your needs, that may have a bigger difference on your enjoyment of photography than yet-another-camera-system. If you are looking for an smaller alternative but not P&S, then there are really really good deals on the older versions of Olympus Pens out there. Here:
Refurbished Compact ILC Cameras | View All | Cameta Camera
I shoot with an OMD, G1, E-PL1 on top of my other systems. OMD is a great camera. When compared to a DSLR, its weakest component is AF.
PS> Dear TPF gods... Subforum?