My worldfile (/var/cache/edb/world) got whiped out. First of all i suspected it was after my upgrade to 1.4 with the scripts, but after asking around a friend had got his file whiped too. I asked him if he had done a upgrade to 1.4. He had installed 1.4 from scratch, BUT he had done a emerge -e world to build with other CFLAGS. I did a emerge -e world after my upgrade with the scripts to 1.4. I'm not sure this is what actually did it, but that seemed to be the thing we had in common. I cant remember what version of portage i had, but it was a month ago.
Only reason I can find in portage for this is an out-of-space condition when it tried to write the world file. Not enough information otherwise, and it's only accessed in two places anyway.