I had this idea while working on the osm.
The original idea was a semantic web osm interface that I wrote about before.
it is an xslt. But my idea is to place the filtering in a proxy server.
like greasemonkey for firefox, but server side.

Here are the related ideas from a chat:

how about a semantic web proxy
that you would use as the proxy server forall your web apps
but would allow for a semantic markup of all the data that passes
grddl, scraping etc
you could feed into it more data about whay you are doing
I mean a proxy server/firewall is used to serve webpages
it gets addresses and supplies data
all the browsers and webapps can be configured to one

so, if I want to make a semantic web extractor for faceboox , for example
I could do that on the proxy server
it would see that someone got a facebook page
and call the right scraper function to extract the data from it
it could even add this data into the html (rdf in html)
or add in java script funtions to display it etc

squid for example it a commonly used program

.wik proxy server
"In computer networks, a proxy server is a server (a computer system or an application program) that acts as a go-between for requests from clients seeking resources from other servers." - http://en.wikipedia.org/wiki/Proxy_server
.wik proxy server squid
"Squid is a proxy server and web cache daemon." - http://en.wikipedia.org/wiki/Squid_(software)
so an rdf proxy server that does griddle and other nice things

I mean use squid, and add in filters

the client would choose to use it
for example. if i want to get the facebook data in foaf
I can use the hypothetical facebook foaf filter
for the proxy server and then just go to the facebook page
and some scripts can be activated on the squid server

More to come.

mike