The topic of in-body vs lens Image Stabilization (IS) has been talked to death, but I thought I would add my two cents. The only camera that I owned, and had in-body IS was the Pentax K10D. Sorry to say, but it was not as effective as I was hoping for, and certainly was not even close to the lens based stabilization of Canon lenses that I am familiar with. After the experience with K10D, I am a bit wary of cameras with in-body IS.
I am sure with newer generations of in-body IS is much better than the first generation that was in the K10D, especially the advanced one found in the Olympus OM-D EM-5. But I feel more confident using lens based IS, as the effect of IS is clearly visible in the viewfinder and I can judge how far I can go before pictures will start to look blurry. I have not used the EM-5, so I can't say how the viewfinder will show the effect of IS. I like the fact that in-body IS will work with ALL lenses attached to the camera, and this is especially useful for lens junkies like me, who uses mostly manual focus lenses. An effective in-body IS system is a godsend. Though I still believe lens based IS is more effective, I really want a camera with in-body IS that's comparable to lens based IS, and currently only the Olympus EM-5 is competitive in this regard.
I am hoping the price of the EM-5 will drop by Christmas, which will push me to buy one :)
Nick Nack - Canon Rebel XSi & EF 100mm f2.8L IS Macro