Micro Four Thirds cameras protect the sensor with an anti-dust mechanism that was originally developed and patented by Olympus for use in their Four Thirds DSLR range. It has a proven track record and is widely acknowledged as being the best and most effective dust reduction system, bar none. However, even this system is not 100% infallible and there is a fair chance that most users will encounter a stubborn spot of foreign matter that refuses to budge from the sensor at some point during prolonged use. There are, however, a number of ways to minimize this risk. Firstly, always turn the camera off when changing lenses. This will help reduce any static charge on the sensor, which attracts dust in the first place. Also, it means that when you switch the camera back on the Supersonic Wave Filter (SSWF) will activate, shaking any newly acquired dust from the sensor (or, more accurately, from the filter in front of the sensor). When removing a lens always use your body to shield the camera from the wind and keep the lens throat pointing down for the whole time that the lens is removed. Have the replacement lens ready with rear cap loosened to minimize the time that the sensor is exposed. Keep the rear elements of your lenses clean to avoid transporting dust into the camera body. If a stubborn spec becomes apparent after changing lenses, turn the camera off and on several times to activate the SSWF – it might just do the job. With care, your sensor can remain effectively dust free for a very long time. Doubters will always say there is probably dust present but you just can’t see it. My reaction is, if I can’t see it I don’t care! I’ve used an Olympus E-3 regularly and with constant lens changing for over 4 years; before that an E-500 and an E-510. More recently I’ve used an E-PL1, E-P3 and E-M5. I can’t really count the E-PL1, however, as I used it with a kit zoom and never changed lenses. The others, however, have all had regular lens changes, particularly the E-3 over an extended period of time. I’ve never, ever, been aware of dust on a sensor or had any cause to clean one.