This page is not meant to be an analysis of Gmail, but while you are at it, please read the privacy page and the terms-of-use page for Gmail. Note that if you delete an email, Google may mark it so that it is invisible to you, but might not really delete it. And if you terminate your account, Google does not guarantee that they will erase your emails. Google decides what to delete and when, not you. It's none of your business.
While Google brags that no humans will read your emails, the entire Gmail program will involve extensive automated profiling of you as an individual. Google will be sharing the non-identifiable portions of your profile with anyone they choose. If the ownership of Google changes, or there is a merger, the entire personally-identifiable profile will be available to the new owners or partners.
The Register highlights another problem, the ability for Google to link your emails to your search queries, which Larry Page explicitly didn't rule out:
"Once users register for Gmail, Google would be able to make that connection, if it chose to," Pam Dixon, head of the World Privacy Forum told the Los Angeles Times. "And if Google ever compared the two sets of data there are some people who would be chilled and embarrassed." Richard Smith, formerly at the Privacy Foundation pointed out that "Google kind of makes it easy to connect all the dots together."
Rather than allay these fears, Google's accident-prone co-founder Larry Page refused to rule out a future policy of 'joining the dots'. A simple "No, Never" would have prevented much of the damage. But asked if Google planned to link Gmail users to their Web search queries, Page replied:
"It might be really useful for us to know that information. I'd hate to rule anything like that out."
I don't know for you, but the idea that one can crawl my private correspondence to profit from it makes me sick. Even if they're using machines to do so. Google has definitely a strange idea of privacy.