Well, I tried PENs and Panny Gs and found system limiting to my needs, no fast primes or zoom, no decent bokeh producing lenses, higher prices compared to APS-C lenses in same category (e.g. you can get Canon 100mm macro in nearly half the price of 45mm macro) and limitations on AF Speed.
This is not rant about the system, I know its good probably excellent for specific uses and offers HUGE size/weight advantage over thier APS-C siblings.
But the moment I tried making it ONLY system its limitations started showing up more and more. So I am getting a feeling it will take couple years before one can think of m4/3 as main stream (not for pros) photography tools. Till then one will either have to have two systems or Stick with DSLRs if you don't want to compromise on lenses/IQ and ready to compromise on weight/size. and this seems to be not limited to m4/3 but to all mirror-less cameras wether its Pany/Oly or Sony or ricoh.