Your phone (if you are using a smart phone) has likely been building a personal user dictionary every since you turned it on the first time.

MS Office has been doing the same for a really long time, perhaps decades. Pretty sure all of the big 3 browsers have been collecting this info as well to various degrees. These 'personal user dictionaries' have been part of the software you are used to using.

Windows 8 has this on portable devices and it works famously while e-mailing or texting. Apple iOS as well since at least iOS 6 I believe. I've never had an Android phone so I don't know if it's in there, but confirmed in Windows 8 on the phone and at least in the text messaging feature of iOS 6 and above. These are the 'suggested' words that appear in various places while you are typing. That's your personal user dictionary. It's really not a dictionary in the sense of providing definitions, it's a personal commonly used word list and sequencing.

One simple example: I live in Colorado Springs. In my Windows 8 phone as soon as I hit a space after typing 'Colorado', 'springs' is in a short list of suggested words. There's also some kind of cloud reference as well as my own personalized list

It makes complete sense to integrate it into all Windows releases for all devices.

BTW - I just confirmed that Win8 has been doing this since 2012. See here: http://blogs.windows.com/bloggingwindows/2012/12/06/the-secrets-of-the-windows-phone-8-keyboard/

Here's one snippet of the article on how they build the word lists (erroneously called dictionaries):

"How did we build them? You helped us! Remember the little checkbox during phone set up (and in Settings) that talks about helping us improve text suggestions and build a better product? When someone gives us permission, we collect anonymous typing data—free of passwords, names, numbers, and other personal info—to help create and test Word Flow."

Here's Apple's latest iOS 8 describing basically the same feature:
https://www.apple.com/ios/whats-new/quicktype/

Doesn't look like Android has a user-specific word suggestion/tracker built in from what I can tell.

As with any information technology, it can be used for good and for evil. I will say that I'm thankful for word suggestions on the Win 8 phone. E-mails and texts are 'muy rapido' compared to my iPhone 4s.

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