Hi All!
One thing I've noticed is that if you have a book with oddly-named chapters -- like in a story collection forex -- calibre will still add the chapters to the TOC, but it doesn't always put a page-break between them.
I found a way to make it do that. Mind you, I've only tried this with books from Baen/Webscriptions (I tried it with LIT, PRC, and HTMLs extracted with ConvertLIT), so I don't know how well, or even if it'll work with books from other publishers.
In the Conversion menu (either while converting, or, like I did, in the conversion defaults) go to the "Chapter Detection" section, and in the box labeled "Force page break before tag:" put in the tag
[a name]. When you convert, your chapters will all start on their own shiny new page
I know this isn't exactly earth-shaking in the tips and tricks department, but it does polish up the layout nicely.