Byron Lahey and other researchers at Arizona State University are working on this all terrain iRobot modification. He writes:

Robot Create robots are easily programmable and expandable in their functionality, but can only travel on a very limited varieties of terrain (carpet, hard flat floors and other typical interior domestic surfaces). As part of the Arts, Media and Engineering program we are working on systems related to the Mars exploration rovers. To teach about these systems and allow students to test and explore terrain navigation and mapping with robots, we needed robots with expanded terrain navigation capabilities. This video demonstrates an early prototype modification of the iRobot, comparing the performance of a modified and unmodified robot traveling on a rocky surface.

This video first shows how epicly the standard iRobot Create fails on a non-flat surface, then shows how his mods make it work better. Here are some photos of the modifications.