Do a security audit of Onion Browser
There exists a web browser for iOS that uses Tor0. It costs 0.99 USD from Apple's app store, but it is open source. The code is hosted on Github1. This project is actively maintained, with the last update being made on May 18, 2013 (The main page mistakenly says May 18, 2012, but the description says it has an update to tor version 0.2.12.4-alpha).
The project already maintains its own list of known issues2. Some of them (like # 26) already make me squirm. However, if Tor is ever going to make its way to iOS, working with someone who has already put considerable work into such a project might be easier than starting from scratch. The developer seems open to working with Tor people because (1)he's open-sourced the project and (2)he claims that he is donating a percentage of the proceeds to the Tor Project.
From responding to help desk tickets, I can say that there is considerable user demand for Tor on iOS. I think it would be great to make a list of things such that we could say "If Onion Browser stopped doing X and did Y all the time, the Tor Project could recommend it to users."
If there are other concerns here I am missing, please bring them up/modify this ticket/whatever.