The topic should be unsettling because anyone surfing the web, especially in seedy and untrusted sites, can easily be turned into an unwanted scraper or even a web spammer for that matter with combinations of commonly used web technology.
Most of us that block scrapers and form spammers work on the premise that scrapers are primarily operating out of hosting centers, therefore we block massive ranges of IPs thus creating a firewall between our web sites and malicious hosting center activity.
Unfortunately, the game has become much more complicated as some of the scrapers are combining technologies in such a way that a naive surfer is facilitating scraping and spamming from his own IP address without having an infected machine, it all happens in the browser.
The form content that is sent to a 3rd party is hidden from view, you would never be the wiser, and could even be combined with a another form on the same page to mask a possible 3rd party site alert under the guise of clicking "search", "feedback", etc. not to raise suspicions.
Now, let's expand on that simple concept and apply it to AJAX which can do all sorts of interesting things.
Many higher end technologies can interact such as AJAX, Flash and other technologies, and you can easily create a combination of technology that will collect data from a 3rd party site and send it to the scraper using the surfers IP address.
Fortunately not a lot of people know how this works which is why I won't delve into specifics to avoid more of this from happening.
Suffice it to say that it's easily possible to misinterpret and block innocent residential customers that have become unwitting pawns in the online game of cat and mouse.
[edited by: incrediBILL at 9:57 am (utc) on Jan. 21, 2009]