I like the opt-out method;
1. Know the system exists in the first place.
2. Know it's possible to opt-out.
3. Know where to go, to get the opt-out cookie.
4. Download said cookie.
5. Remember that if you clear your cookies (which most of us do, from time to time), you'll be automatically opted back in, and have to repeat the whole process.
I'm also amused by how BT arrived at the 15-20 users (the ones which noticed there was something going on).
In BT's own words, it seems they saw 15-20 posts, on internet forums, relating to this sort of thing, and assumed those 15-20 were the only people to detect it.
I also note they acknowledge the system is by no means fault-free (the best one being the ability to get Internet Explorer to use up 100% of the CPU resource, when visiting a site which has loads of html "anchor links").
The whole document, if genuine (and there's nothing to suggest it's a fake), is very hard to defend - even by certain people who think the sun shines out of BT's bottom.
Ade
ADSL2+ with BE
DL Sync Blimey....4707kbps now!
UL Sync 1088kbps