Simple is good, but a few enhancements could help this front runner from future competition.
- Undo is finicky and sometimes you can make a stroke in a session that you cannot undo.
- landscape is not a friend, the page gets cut off; Penultimate scribbling is mainly done in portrait mode.
- one review mentioned issues with many pages PDF export, but I have yet to confirm.
As a user of PhatNotes, FastFinga and Tanzaku Pad, all very functional in 2x mode, Penultimate has the early mindshare lead.
That TUAW review, helped, but that early adopter price should stick around to fend of any competition for a while.
I think it is worth it for the quick todo list or scribble.
Adding a typewriter text tool may detract from the paper and pen feel, but a way to tag pages so as to find previous scribbles would enhance the digital ink beyond a paper moleskine notebook.