Privacy certainly ranks as one of the primary reasons many are opposed to Google and Gmail. Another concern is content appropriation and monetization.
I was a big fan of Google when they first came on the scene. I loved the relevance of their search results, plus all of the cool programmer-centric tools they offered. I didn't mind when they introduced AdWords – it seemed like a valid way for them to make money. We had legitimate search results, and we had "paid" search results, and the two were clearly separate.
At some point, though, Google stopped being a search engine, and became – something else. They weren't just indexing my pages (content I authored and own), but were storing complete copies on their own servers. Moreover, they use all that cached content to drive their advertising systems. I don't recall ever giving them permission to copy my copyrighted content. When did I become one of their "content providers"? Where’s my payment? If they are profiting from my content, shouldn't I get a cut?
Interestingly, I see the "Google Model: How to Profit from others' Content" paralleled in many online systems, including user forums such as Daniweb. It's certainly appropriate for a forum operator to sell advertising, and to dedicate page real estate to show ads. However, many sites (including this one) have crossed the line into selling off the very words members type. Again, a line has been crossed: sell your screen real estate? Fine. Sell my words, without my permission and without payment? Not Fine.
Aggressive monetization of third-party content is one of the saddest aspects of how the web has evolved. Keep your ads out of my posts, and keep my pages out of your cache. At least Google honors the "noarchive" meta tag. Where's our "no-IntelliTXT" tag?
In the early days of the web, there was the phenomenon of using HTML frames to wrap someone else's pages within your own. This caused considerable outcry, some lawsuits, and the proliferation of "frame-busting" scripts. Yet for some reason, we let Google cache and serve all of our content, in fact build a multi-billion dollar business around content theft, and they enjoy near cult status.
Pay to use Gmail? Google should be paying Gmail users and web site owners for the content!