> to see if anyone was leaving my books
> somewhere (still haven't figured out if I
> can do that).
Sure can! In the left sidebar, click on the category "books" That will expand and let you click on the subheading "search books". Plug in the title, author, or isbn, and wait for the site to come back with an answer.
If you want to, you can certainly register copies of your own book, leave them lying around, send them out on bookrings or bookrays, or offer them up for trade, for postage, or as RABCKS. (RABCK = Random Act of BookCrossing Kindness, a book sent or other deed done with no expectation of return, just to be nice.)
TexasWren maintains a list of Bookcrossing authors - if you do a search on her screen name (under "people" in the left sidebar) I'm sure she'd be glad to add you and your book to her list. (And if I've flaked out totally and given you the wrong person, I'm sure she'll know who to refer you to...)
Welcome to BookCrossing!