Um, as a former Googler (whose office for a while was right across the hall from the GMail developers), the only things "monitoring" GMail's emails are computer programs, which are only doing the sort of things you note; picking (hopefully) appropriate ads to place next to the messages, completing familiar addresses, etc. No human is doing this, and the programs are only doing what they're intended to do; they don't flag interesting messages for people to look at or anything.

Yes, it is possible for a very small set of humans at Google to look at one's email. And if they did so for any reason other than to fix technical problems or the like (and that requires approval to boot), they'd be fired. That's the case for any email program; there's always some level of programmer/administrator/tech support which can look at their system's email. But the good ones (and this is for a pretty minimal level of "good") have precautions and procedures in place to keep this from happening without *very* good and necessary reason, and fire anyone caught violating them.

Oh, I didn't think a human was checking out my e-mails -- heck, the staffing for a non-computer-program monitoring system would provide full employment for the world's population. I do know there are people to whom g-mail is undeliverable because they don't even want to RECEIVE anything via the service.

My confort level with it all? It's high enough that it's my primary personal e-mail service.