Are there any options for porting apps from iOS to Android and Vice versa?

I think it's really only for games where the whole interface rendering is done by the program. In this case, it is sufficient to keep easy compatiblity layer, which provides the output to the screen and receiving events (type of driver: "display in iOS", "output to the screen in Android).
\r
For "no games" this option not suitable — rendered hands the controls will look crooked and don't fit in the interface guidelines (and, hence, the apple-censorship does not take place — at least). Everywhere your front-end tradition, what to do. Of course, the application logic (model) can be shared, but rewriting the interface for the two platforms will take the most time and would mean that it is not multiplatform.

For my game I made as it was written above a thin layer that interacts with the phone functions and deals with rendering. So I have a port on Linux/Win/iOS/Android, via links to the sources folder, we get 4 of the project. The only big problem with audio in Android, as there is no direct access to alsa, the only hope for version 3.0. Still have problem with multitouch on many. (G1,G2,Hero,N1), but it is solved in a specific manner spaced controls on a control(for example: lower left and upper right corner).
Links on the issue of sound:1,2,3
\r
PS: Can gather and write an article.

View to the side www.appcelerator.com/, apps of course get thicker than if you write native code, but at least the problems with porting.

Look at Airplay SDK

Thank you very much!

MoSync (C/C++)
\rRhomobile (Ruby)