Ah, never mind. Updated the drivers after a bit of googling to 14.4 "beta" from AMD. Works now. Also seems to have fixed some (unrelated to Factorio) screen tearing / v-sync issues I was having with the 13-branch drivers previously.

Just got interested in this game and tried the demo, but alas, am sad to report that I'm getting this exact same problem. Only random letters here and there, some menu screens totally void of text. Demo version 0.98/x64, Ubuntu 12.04, AMD HD5750 graphics adapter, AMD proprietary Catalyst drivers 13....