I've used h1 for chapter titles, h2 for sections within a chapter. The page appearance is good. But the customer has sent it back - she's looking at the Contents panel in ADE and wants everything top-level. (I've given her a functional inline Contents page, but there's no point in arguing. Enough trouble explaining how she can't have it looking EXACTLY like the printed page in other ways :-)
I changed all the h2 tags to h1, recreated the toc, edited the book to back how it started. Could I have done this more easily by direct editing toc.ncx? I can't see from examining it how the hirearchy is set.