Microsoft just released an update to the free OneNote app for Windows 8 that has added the ability to draw on your touch screen using your finger. "Many of our users expressed the need to be able to draw on the touch devices that do not ship with a pen. With this update to OneNote for Windows Store, now you can draw with your finger!" Microsoft stated.
If your device does not have a touch screen, you can still use the feature with a mouse by following the same instructions above. Inking with a pen still remains the preferred experience. You can flip between pen and touch without much hassle and pan the page more easily.