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On the Sony side of the ledger there's built-in image stabilization accomplished by using sensor vibration. This has been shown to be every bit as good as stabilization systems built into lenses. The big advantage though is that it applies to any lens mounted, not just specific lenses. And though wide angle lenses tend not to need stabilization as much as long lenses, having these stabilized as well is a real bonus.
This is a sentiment I see expressed frequently. I think it is misleading and should always be qualified. When shooting with long telephotos, having image stabilisation in the lens is extremely valuable, having image stabilisation in the body is worth far less. The only exception would be if you are using a camera with an EVF, such as the Panasonic G1. The reason is simple, you need a stable image to focus (somewhat when using AF, very much when focusing manually); stabilising the sensor doesn't help with that.
No matter what the focal length, I find it easier to compose when the image isn't jiggling around, but that may just be me - heck I actually like the "swimming" motion caused by stabilisation.
The paradox with Panasonic's M4/3 system is that it doesn't benefit by placing stabilisation in the lens - quite the reverse, in fact, for the reasons Michael gives above - but Panasonic opted to do so. In that regard, I think Olympus may have the more compelling M4/3 body offerings. Indeed, the lack of sensor-based stabilisation is the major reason I haven't been able to convince myself I should buy a G1.
