I have a very complete 1DSIII system, with lenses ranging from 17mm to 500mm IS. In late 2009 I bought an A900 and several lenses. I now have 11 lenses, and have not used my Canon gear since. I keep it because of my 400mm 5.6 L, and 500mm f4 IS, as there is no comparable Sony lenses. I use it because of its (comparitively) small size and weight. It is also more like my film days, as there are MINIMUM buttons/menues/sub menues. In camera stabilization is wonderful. I bought VERY cheaply on ebay Minolta 20mm f2.8, and 50mm f1.7 lenses. I even bought for a knock-around lens the Minolta 35-70mm f4 for $28!! No kidding. I also have the Zeiss 16-35, 24-70, and Sony 70-300 G lenses and they are, in a word, superb! Also I bought a used Minolta 500 f8 mirror and it is amazingly sharp (with auto focus and image stabilization).
You can't go wrong! Also worth exploring is the feature of multiple DR images prouced simultaneously. You take one shot and the camera produces three brackete images. I have not playe with this yet.
Very best, and good luck!
Dave Gurtcheff in NJ