I might do that depending on the books, though admittedly I'm trying to pare down on the book accumulation (unlike the card accumulation ... yikes). I think shipping books will be a little pricier even when using media mail, but if it gets the cards one wants, I suppose it's worth it.
One thing to think about is value if that's what one considers for trades. Some paperbacks can be found for a dollar or less at flea markets or yard sales, but other books tend to be $4-5 or even up to $20. Sending that much worth in cards for one book might be a tough trade to make for some. It'd have to be a heck of a book for me.