Joining in this a bit late but I have a Sigma 70-300 APO DG Macro which I use with a Nikon D40. I had a good summer with it in 2009 and was doing quite well this year until the Little Gransden show when the whole shebang locked up and it wouldn’t release the shutter, focus or anything else. I took it back to the dealer in Cambridge who returned it to Sigma and it’s back now , repaired at their cost as it was under guarantee. There was no explanation with it but it does seem to be working quite well but for how long? No airshows to check it at this time of year.