Why is this incredible?
There are quite a few drawing and sketch apps, but
Sound paper has done a really excellent job of mirroring the functionality of a LiveScribe Pulse pen by allowing the drawing to be synced to audio.
You can tap the drawing and the audio starts playing near that position.
Tapping a pencil icon at the upper right corner switches to drawing mode and you can begin drawing right in the middle of your text.
Drawing dramatically increases SoundPaper functionality.
The interface is quite minimal but done very cleanly in that a double tap will select a single stroke and a single tap will select a stroke and its adjacent neighbors.
You can make a single strikethrough stroke and select it with a single tap to delete multiple strokes, but the ability to group strokes to move them around would help.
Also I would still like a date time stamp insert option though or TextExpander support.
All in all however right now Soundpaper is the one to beat.