If atmospheric light scattering is enabled, random buildings breaks:
This is with all shaders maxed. As you can see, I'm still getting 21 fps...as long as none of those stupid over-detailed airliners are in view. If I disable scattering, the buildings reappear.
Also, when I paused fgfs to make the screenie, the Launcher crashed and had to be force-quit from the Dock. After doing that, fgfs was still running, and flight resumed when unpaused.
iMac11,2, Core i3 3.06 GHz, 4 GB RAM, ATI Radeon HD 4670 256 MB VRAM, OS X 10.6.8