elenar said:
When something happens once, it's a coincidence. When something happens the same way more than once, it starts being a pattern. Two incidences aren't enough to establish causality, but they're enough to strengthen the correlation a fair amount. In other words, one eyewitness may be embellishing or misremembering, but 2 eyewitnesses telling the same story are more likely to be telling the truth.
Aside from the fact that there have been many experiments showing several eyewitnesses can misremember exactly the same thing, we're talking about a very different situation here, something whereby negative outcomes may or may not occur between two different groups and we only have anecdotal date from a non-random selection of people, almost all from one group, to go off.
If I can get two people who don't use a peer blocker and have never had an ISP letter, can we start to assume a correlation whereby NOT using a peerblocker means you don't get ISP letters?
People using something which is supposed to protect them from a particular event are more likely to offer their experience than someone not using it, we see this in all kind of pseudo-medicine and superstition. People who use a homeopathic tablet which is supposed to ward off colds are likely to notice and tell people that they haven't had a cold all winter. People who've not been doing so are unlikely to even think about the fact they haven't had a cold for a certain amount of time. This is how people can make millions selling empty sugar pills, because people say "Well, all these people say it works, they can't all be wrong, can they? I mean, if it stopped one person having a cold it could be coincidence, but when you get two, or three, or four, there must be something in it."
You've also got to take into account the fact that, even if companies haven't bothered to go to the minor inconvenience of downloading peerblocker themselves, looking at the IP ranges it blocks and simply doing their scanning from an unblacklisted addess, that there's little to stop them doing it tomorrow, or the day after, or the week after.
If I worked for some of the dubious legal firms sending out the letters, I'd be setting my search running on my home PC using a domestic broadband provider.