What about Facebook? A few weeks ago I had a situation where Facebook contacted me about a job, and it appeared that Facebook may have been reading (or at the least mining) private messages related to my startup ( http://news.ycombinator.com/item?id=3035376 ). A Facebook employee replied to the thread but wouldn't provide details.
(I am neither a Facebook employee nor can I speak for them.) I really think that was just coincidence. Considering how many people talk about startups over Facebook messages and how many people have been contacted by Facebook recruiters, there's bound to be at least one person who was contacted by a Facebook recruiter a day or two after talking about startups. It'll seem mighty suspicious to that person, and they'll…
Receiving an email from Google or Facebook is nothing special.