Well i tried out Olympus EP1 + 70-300 for birding. Not too bad actually. The high iso really helps here. Autofocus as usual is slow but you have to anticipate the movement of the bird. But the weight of the EP1 +70-300 is really light.!! it is a very compact setup. Try comparing a D700 + 600mm lens and you will know what i mean. Having say that i does not mean EP1 is better than D700. What i am trying to say is for casual shooter the EP1+70-300 is sufficient. If you are a commercial shooter by all mean get the D700.