As someone who's done a lot of data mining, I'm always surprised to find that sites with lots of data don't do this. Your output generator just needs to randomize some class names and throw a couple of pointless elements around the place to make it MUCH more difficult.

There's one site I've scraped that has code like this: <div class="name"><span class="first_name">...</span> <span class="last_name">...</span></div><div class="street_address">...</div>