I started development on an anonymous chat, where people sign up with their BTC Address.
The ownership of the address is verified by entering the balance of the address.
Terrible method. I could easily sign up and claim to be Satoshi via that method just by looking up his address on Blockchain.info.
Also, this chat will only be anonymous if you generate a fresh address for it. Worth pointing that out, and it probably wouldn't be too hard to end up tracing either