OneNote is Microsoft's must underrated app, in my opinion. I've always enjoyed the inking features on Windows tablet PCs. Now iPad users can get in on the fun too.
It's surprising that it's taken so long for drawing support to come to the iPad, given the nature of the tablet. (Android tablets already have digital ink.) But the new features look great.
There's a new Draw tab on the ribbon, where you can select a pen, marker, highlighter, or eraser and choose from four default colors (and 20 more via the color wheel) as well as change the line thickness. So now you can sketch or doodle on any OneNote page and combine ink with photos and text: