Andrew Stacey wrote the afterword for his article Matrices in Codea:

This article, with the exception of this afterword, was written entirely on the iPad in LaTeX using TeX Writer. This made it easy to include code snippets from Codea programs and screenshots. TeX Writer produces a PDF which can be downloaded. The resulting TeX document was converted to a suitable format for including in my website (MarkdownExtra+iTeX) by a newer version of the internet class.

Who said iPad can't do serious work?