I have read a couple of articles about the using statement to try and understand when it should be used. It sound like most people reckon it should be used as much as possib
Personally, I have used at least 3 layers (Connection, Command, Other) a number of times and I see absolutely no problem with it, but as you have already hinted at, eventually there will be a problem a readability. As with other nested constructs, you may need to balance efficiency with maintainability. That is, you don't need to necessarily sacrifice efficiency, but there is often 'more than one way to skin a cat'.
That said, you would be hard-pushed to generate 10 nested layers!