[antonyl]

How would this happen? Are you sure it's not just the frequency illusion? DNS? (Although that I think would only give you domains.)

[baby_souffle]

Proximity to other rf emitting devices? I always assumed this is how those "I googled x and discussed it with a friend over dinner and now my friend sees adverts for X" type things work.

[colordrops]

It's not frequency illusion, it happens daily with very specific things, like obscure climbing gear for instance.