People do have problems with deep bedding, but it may also be the type of bedding that is used, and not simply that it was damp or a watering system issue. Mike's deep leaves are very different than someone else's deep straw or hay, and while he is successful with leaves, in my opinion the system remains to be tested fully with more material types than this. I'm hopeful that you are correct, Nick, and that deep bedding can be used successfully, as I think it's much healthier for the birds. What does your friend use for bedding, and how deep is it?
If you're having trouble with deep bedding it's probably because the bedding was damp when you put it in and it never dried out, or your watering system needs an upgrade.