I only write E-Mails to authors here, because mails give you the chance to really get in contact with her/him. Ok, I could do both, mailing and reviewing, but I'm a bit lazy.
I didn't count the number of people I mailed, probably ten, and have a regular "conversation" with one of them, and it is developing better, than I hoped for.
I've been here for only a few weeks, so I seem to be very lucky