OK, point lights are now disabled in r3027 for ATI users, those were the cause for the crashes. I installed Debian on the ATI machine that I have access to in the hope of running Valgrind and maybe tracking down a problem on our side, but it spammed the log full of errors from the driver so there was no hope of singling out a relevant failure. This even seems to be a somewhat well-known issue, and after that I simply cannot take the ATI people seriously.
(To be fair, I recall Valgrind reporting a couple of errors for NVidia drivers too, but nowhere near that quantity.) I also wanted to test whether the gamma-reset bug (fullscreen/8-bit) that plagued ATI users on Windows a while ago also existed on Linux, but the gamma slider did nothing in the first place. *Shrug*