This service is awesome. I just used it for the first time to convert some Namecoin that's been sitting in my Bitminter account into Bitcoin. Very quick and easy and great UX.
I've heard some talk on the boards of a web based BitShares wallet in development. If bitUSD is integrated into ShapeShift, it would be fairly easy to integrate into the web wallet, via Shapeshifts API, to allow new users to deposit BTC and receive bitUSD in their wallet. Users could then withdraw bitUSD directly to BTC.
Integrating ShapeShift into a web wallet would also be a great selling point for getting bitUSD supported on their platform.