Seconded, but I'd like to expand on it just how impressed I am with it. It doesn't support PowerPoint or Word Document formats (yet), so you'll need to convert those to PDF.
The work flow is easy. Notability supports DropBox, and two other services (not iCloud yet, and not SkyDrive). Put your "raw" note files into DropBox, and then import them from within Notability. Notability allows you to organize your notes into sections if you want. Once you're done with your notes, you can send them back to DropBox. I have two folders within DropBox for this purpose: one for the unedited notes (to be imported into Notability), and one for the annotated notes (exported from Notability).
But how it is for actually writing notes? Amazing. I have one of those capacitative pens that I use for note-taking. The "tip" on those pens is rounded, and it's very difficult to write small on the iPad. Notability's solution is to have a "magnified" view: a resizable box can be dragged around the document, and the lower fifth or so of the screen represents what's in that box. This allows you to make larger strokes for legible writing, but it appears on the document as regular-sized text. On the right side of this writing box is a green-colored strip, and when you make a mark inside of it, the magnification shifts over so that you can keep writing. Once you hit the edge of the page, it shifts down and across to the other side. It's an incredibly smart implementation.
I had one class where we had to write a lot of things very quickly, and I didn't have any paper on me. That forced me to use the iPad, and that's when I discovered that I can write almost as quickly on the iPad using Notability as on paper. Thanks to Notability, the iPad has replaced paper for me.
I saw another classmate with a different note-taking program that looked like it had a similar magnified view for writing, but I don't know which program he was using. Notability does a very good job, though, and I can highly recommend it.
