What I've found lacking on the iPad is apps that are suitable for structured, long-form writing similar to things like LyX. I can write Markdown or LaTeX by hand in a text editor but much prefer a graphical environment, and none of the available word processing apps support styles, cross-references, or any of the other things I need for academic writing.

I've actually been working on an app which supports these features for the past few months and hope to release soon. It's at the point where I'm looking for some feedback on UI & functionality from anyone who does a lot of academic or technical writing. If you're interested, drop me a line (kellypmk@gmail.com).