I see these all of the times, especially when visiting sites that have torrents and the like.
I've never fallen for one, wether it be online or one of the ones that call your phone. The best thing about not having a shit tone of friends is that there are only a handful of ppl who actually call me (as opposed to sending a txt) so i don't even answer my cell if i don't know the # calling.
One funny one though i got on my phone. The 2 major cell providers here in Ontario aer Bell and Rogers. I'm on Rogers and got a call about how my Bell account had been selected to win a prize