> "A lot of them already hijack port 80 and inject random junk in there..."

That's a pretty bold claim. Other than free wifi at hotels, I've never seen an ISP use transparent proxying to intercept pages and serve ads.

Do you have any examples?

My provider at home, Rogers Cable (Toronto), will inject things in the pages you see when you're approaching your bandwidth cap. It's extremely irritating and somewhat worrying.

Basically they mangle the HTML and slap in their own banner which means they must be doing some kind of stream inspection and processing to manage this. I do not have a proxy configured, and requests don't indicate that this is being done.

I would be VERY interested to see a packet capture of the same page when you're under and near your cap.