Brilliant Marketing Hack or Book Spam?

I just dropped off some books at the library and had this idea. What if
I went into the business and computer section and placed my business
card in the books as a sort of book mark?

Imagine it - you're reading a book titled "Getting Started In Business"
and out drops a card with the name of a guy who writes custom software.
Brilliant, you think. And even if you don't call the name on the card,
at least you have a handy bookmark you can use.

Could be highly targeted and relevant marketing. Could be rude and
obnoxious book spam.

So far, I'm leaning towards the spam side, so I probably won't do it.
But still, could be a good idea...

--Ben