I just bought my first app on the Apple app store for iPad. It is called Notability. I have owned an iPhone since April 2008. I have never spent any money at the app store before this.
I have been sitting on a 25 dollar credit at the app store since I bought an iTunes card off my daughter. She got two as a gift. She had a 10 dollar one as well. The 10 dollar iTunes card had expired. That was a poor move Apple. I strongly recommend that, should one be so silly as to purchase an iTunes card, or so unlucky as to get one as a gift, add it to your account immediatley. Once again, Apple marketers, you are the worst.
That story aside, at school conferences, the math teacher did our conference review on iPad hooked up to a Promethean board. The app he used was called Notability. I was suitably impressed.
I have used OneNote, and also the ill fated original Moleskine app. Notability does a much better job.
One problem, it exports to pdf only with a white background. So, do not use a colored background and white ink.
I also got the new MoleSkine Journal, which is much better than that piece of junk Moleskine app. The original Moleskine app has been pulled from the iTunes store.