Input is only logged when the input would be used for predictive touch and builtin spell checking.
Unless you enter everything with the touch keyboard then this does not apply. Even so, you can pretty easily disable the actual services.
http://windows.microsoft.com/en-gb/windows/preview-privacy-statement"when you open a file, we may collect information about the file, the application used to open the file and how long it takes to use it for purposes such as improving performance (e.g., to help retrieve documents more quickly), or
when you input text, handwrite notes or ink comments, we may collect samples of your input to improve these input features, (e.g., to help improve the accuracy of auto-complete and spellcheck)."
Just putting it out there, it doesn't sound like it only applies for touch keyboard.
