Thus far, Jeff Bezos has not sent his henchmen out to my house to rough me up.
It's been discussed here a bit. Do they have the capability to detect? Yes, I'm sure they do. Up there in the Kindle Developers section is some info about Amazon/Big Brother and the information they store about your reading habits. It is enough to make you want to get out the tinfoil hats.
To tell you the truth I'm not a huge fan of all these new "Social Reading" enhancements like shared highlighting and notes and rating the book for other readers that they keep coming up with. I like my reading solitary for the most part and I keep my WiFi mostly off.
Do they care? I couldn't tell you.
I do know that by the estimates I've read there are about 10 to 12 million Kindles running amok now. I seriously doubt Amazon is going to take the time to inspect all our libraries and try to make judgment calls on whether or not that Un-DRMd document is a book I liberated, something I copied from FanFic.net, the menu from my local restaurant, an ARC book from NetGalley that was sent to me for review, or the agenda for next Friday's Sales Conference ... all of which currently reside on my Kindle.
That would be an awful lot of hired manpower snooping.