Google has today announced that it will be giving you an improved autocomplete experience in Gmail by custom tailoring the predictions in the search box using your email. This means, basically, that Google will scan your inbox to provide you with more accurate autocomplete suggestions.
Google famously already uses the contents of your inbox to deliver personalized advertising while you view it on the web. At least this feature is using that data to improve your Gmail experience.
The Gmail ads are a result of an automated system that reads the subject and contents of your email inbox and then delivers ads based on those topics. No humans read that data, says Google, and the system used to tailor your autocomplete suggestions is likely the same. I’m sure some people will end up having an issue with this further use of your private email data, but it is delivered to you personally and it’s already being used for ads and other things like the Priority Inbox and spam filtering anyway, might as well get more use out of it.
The improved autocomplete function will be rolled out in English first, over the course of the next few days and will not initially be available for Google Apps customers. Additional languages will end up getting support over the next few months.