What advantages does Armory have over Bitcoin-Qt? What advantages does Armory have over Bitcoin-Qt? Just better multisig support? Armory runs bitcoind.
Some obvious reasons:


Deterministic wallet (only need to store the seed, bitcoind's wallet uses a random number per address).
Multisig support with lockboxes.
Paper backups with SecurePrint.
Fragmented backups (you need m of n pieces to get back your wallet)
Offline signing for additional security


There's also a lot more features that are on the way that we'll be announcing (Disclosure: I work for Armory)