They must be useful to some folks - but if you are net savvy they are the net equivalent of Tescos smearing shops and supermarkets everywhere (and holding sites to prevent competitors using them).
Market share.

And whatever they tell you - they are snooping on what you surf too. To make your experience better - HA!

So that 200 aggregator sites can tell me (several times over) they can sell me (at the cheapest) liver cancer, or nightmares or other such unsaleable ephemera. Yea really. That's why they do it. And they got rich on it. If I am asked to find out about liver cancer I want information not books, first. But information doesn't earn revenue.

I don't even allow Flash on my browser - on dial-up it takes 5 minutes to find-out that the movie has no information content, and the text will follow. No it doesn't I move on quickly. Not everyone has Flash and I need to see what all visitors to my site see and I can only do that with basic equipment and installations. And by checking often.

No snoopware at Rouge Towers.

Geoff - if your library has the same kind of PCs as mine - install it on theirs and play with it. The PC is wiped clean when the next person logs on.