DuckDuckGo is already becoming habit, and I'm pretty close to convincing others in my company that we need to switch off of Google Apps, because Google hides important messages from me and doesn't provide support [1]. What else does Google do? Drive? Dropbox is better. Plus? Haha. Google is putting all their effort behind things they're only mediocre at, chasing after the fashionable new kids on the block, and dropping the ball on their core competencies. Maps will keep me around for a while though. However, a maps app that cared about my privacy would win me over...
Every giant sees their peak and gradual decline. Google's just came very quickly. I hope they see a renaissance.
[1] http://productforums.google.com/forum/#!topic/gmail/aU4UUye3...
Maps, as I said, are different.
Even if you're not using Gmail's webapp, it's an entire email infrastructure serving as the backend for Mail.app or Mailbox or whatever you use. At this point, if someone doesn't have their own mail server, they're probably using Gmail.