How would people feel if there was a similar MSN service that did the same thing - do some just trust Microsoft more than Google?
People that don't like Microsoft (i.e. "those Open Source nuts...") tend to worship Google. And it works the other way aroud, too. I don't think there is a "trust" issue here, really.
Google couldn't do this without the ads and they are far less instrusive than banner ads. Sometimes the ads are even useful.
And remember, Microsoft does not provide Hotmail "out of the kindness of their heart." It too is a commercial project, ad supported (I can not believe that the "value added" services account for a significant part of Hotmail's income.)
Why are people worried about Gmail but not Google Search - which also targets ads based on content. And all those websites that use Google AdWords?
Because communications such as e-mail are generally thought of as "private" and subject to different rules than a simple search query. Would you mind if I drop by your house / apartment, open all your mail, and pack in a few ads based on the content of
the private communication I read in that mail? Sure, "real people" will not be reading your gMail, but still, there is a sense of violation there. Perhaps not rational, but still there. Also, it takes away from the experience of reading a letter from someone;
it's an invasion of the experience.