All real (not system mixed) deposits to your address are credited. You control your private keys and can sign messages. Your spending comes from different addresses.

What this means is it gives you the privacy of a shared wallet, while allowing you to do things like hold ASICMINER shares to your address. Best of both worlds

We are also looking into free (up to a certain number of chars) vanity address generation for our users, using Amazon's powerful cloud resources.