Funny shit… LOL… and entirely possible. But this method of using cookies has been in existence for a long time, such as with Doubleclick – and I’d think that if Yahoo were going to try something like this they would do it with GREAT care and advance warning.
I’m not too worried about MSN yet – but you think they could have started on something like this about 5 years ago? LOL… but when they do it, it will monopolize your computer (ie. with Longhorn as you suggested) and the rest will probably find themselves in a bit of trouble.
Meantime? Watch Google as it tries to right the ship – the results right now still stink to high heaven, but at least it isn’t the pre-Florida cesspool. And watch Yahoo who seem to have gotten off to a pretty good start for a “new” engine.