This decision set a terrible precedent.
It made it acceptable for a company to deliver "tailored advertising" by reading all your emails.
But I guess there are few alternatives to the ad-supported business model on the web facilitated by the vast collection of personal data.
Still kind of sucks, though.
More generally most cloud services are going to have the same properties. It would be more useful to define clear bounds of what companies can do with your data and back them up with workable legal protections.
The data mining and the ads are the price I pay for such incredibly useful services, that don't cost me anything but a small bit of attention. And even the ads are good, because they're so nicely targeted.
However, I really appreciate Google's ability to block spam, and I don't know of any way to make that work (at this level of quality) without a centralized service sharing spam-flagging between millions of users.
It's possible to with encrypted search.