Which books should I read to use and understand Mac OS well?
I was in the same position ¾ years ago and went ahead and loaned Mac OS X Snow Leopard: The Missing Manual (Pogue, David. O'Reilly).

It introduced all basic things what an imaginary OS X Snow Leopard manual could had included, albeit it isn't written in a conventional manual style. It is good for OS X newbies, as I was, because it explains even some rather elementary features/operations.

The Missing Manual doesn't cover Windows vs. OS X in a too great detail, which is, in my opinion, good thing as it makes you learn OS X from the ground up and makes you work with your operating system more intuitively (ie. you don't think Windows operations first and then translate them to Mac OS operations, but rather think of how things are done in the Mac OS straight away).

The downside was that the basic aspects of OS X were rather easy to learn with 10+ years of experience of other operating systems. It also introduced the majority of bundle apps, of which some were uninteresting to me (like iChat). The book was relatively fast to skim through.

The best part was the 6-page keyboard shortcut appendix to which I returned more times than any other chapter.

I can recommend the book — perhaps not to be bought, but to be read. If your local library has it in its collection, it's worth a visit.

Note that OS X Lion is due to be released later in this month. I strongly recommend to hold back buying the book now: either wait for a massive price drop or buy the book used; or wait for Lion books to land, if you're about to upgrade.