How can I prevent Armory from getting stuck at "30 seconds" Building Databases on OSX 10.9?
WARNING: Triple-check you have a backup of all of your Bitcoin-Qt and Armory wallets before deleting anything.

Deleting the Armory and Bitcoin data directories (~/Library/Application Support/Bitcoin and ~/Library/Application Support/Armory) and re-downloading the entire blockchain (starting with a fresh bootstrap.dat) in Bitcoin-Qt fixed this for me.