Probably I am bad in describing..
starting point was:
I just saw the topic and thought, OK gonna answer some questions for BTC.. klicked on answer, and ... oh, have to register - for what?! just want to answer and type in the address to be paid for that. You want my email-address - why, I doan need any spam!?
Just signed messages ? Who would receive such signed messages, and where would they be stored ? How would they be published? I think *just* signed messages and addresses would not be enough, because there must be a carrier for such messages. I might be wrong of course. Could you explain how would such system work ?
We want (I'd really like
prolly as optional feature ) valid addresses and proof of ownership for not needing accounts on your site. To verify ownership of an address (which could be used to login without anything like a password, email or any other id) you might crypt a message (or hash of the answer) with the privkey.
Of couse not sole messages but with the pubkey (btcaddress) to enable verification to anyone. That way the answerer can proofe the address he attached to the questioner and that it is owned by him, and he can also proofe for other answers afterwards. Also the function to sign messages is included in bitcoin.org-client.
And noone shall post and sign with an invalid address for reasons of spam because he wants to receive the coins.
an example of account-avoiding is implemented in pyramining. you login with the pubkey of the "online-wallet" and for spam reasons there is a captcha. This also could solve the same for questioners, answerers wont need such a "online-wallet"-pubkey but their own (possibly offline) one.
My point simply is: passwords, email etc. are vulnerable. I doan see why making your service less secure if you like to have trust by users. E.g. bitcoin.de only has a username/password/withdrawallimit to save you from account-stealings, bitmarket.eu was getting better but shows the reset password as debug-info to anyone who asks. Mt.Gox asks for more personal information of users (utilities bills etc.) due to financial restrictions regardless of juristiction or absent problems.
Such flaws can be avoided and save you very much time and bad user-experience. Also I think that would make the service much more popular if you can solve the other problems
(e.g. by voting).