It is worth keeping in mind that by default Windows 8 apps can use your name, location and account picture. If you're not happy with that, it can easily be changed. Press the Win+I keys, click 'More PC Settings', select 'Privacy' and click the relevant buttons to disable any details you'd rather not share.
The new Task Manager also includes a History feature that tracks the CPU time used by every application. If you're wondering what someone's doing most of the time on their Windows 8 system, launching Task Manager (press Ctrl+Shift+Esc) and clicking the App History tab will give you an idea. But if you don't want someone doing the same to you, clicking 'App History->Delete Usage History' will clear all the figures.