This is likely a configuration issue on my own machine. Just tracking progress and documenting, in case someone else runs into the same problem.
OS X Lion, XCode 4.4.1, R 3.0.1,
Seems to have been fixed by updating XCode and reinstalling R 3.0.1 (with homebrew)
I think this came about as a result of installing multiple versions on R on the same machine using homebrew. Installing R 3.0.1 by itself seems to work. Installing 2.15.x at the same time seems to lead to segfaults.