GreaseMonkey: Set to Sabotage the Internet?

Here's my first contribution to the technoculture blog, to start off I thought I'd introduce everyone to a new emerging addition (or even modification) to internet browsing called GreaseMonkey.

Technically speaking GreaseMonkey allows a user to install javascript userscripts into their browser to dynamically rewrite webpages on the fly. In terms that you and I might understand better, it gives you the ability to change the the content of webpages as you load them, replacing context sensitive text and links with your own. Eg. you can visit a page like TradeMe, and have links to eBay search results appear right along side the TradeMe results. Alternatively you could have Telecoms YellowPages website give you links to the exact street address on Wises' mapping website.

An example of modified Amazon page with links and prices to stock of Amazon competitors.

Greasemonkey is like being able to rearrange the aisles at foodtown to set the beer and cornchips at entrance and play your own death-metal over the intercom.

Although the idea has been around for a while and Google has even caught on to it, by using the Google Toolbar a surfer can turn all ISBN numbers on a page into links to Amazon's listing for the book. As one developer points out in this screencast, he took this idea a step further, making the amazon webpage display links to his local libraries holding on the book (this even supports Voyager!).
Some bloggers are predicting that GreaseMonkey will absolutely destroy existing business models, set to destroy internet advertising and marketing (again, since popup blocking already did that). Already there are scripts available to link from Amazon to a BitTorrent of the searched movie title.
The question I'd like to put to the rest of you guys, what do you believe the rules and ethics with this technology should be?


Valuable Links
http://weblog.infoworld.com/udell/gems/intermediation.html
http://dunck.us/collab/GreaseMonkeyUserScripts
http://greasemonkey.mozdev.org/
http://simon.incutio.com/archive/2005/04/11/etiquette