Again, wallets don't get tainted, transaction inputs do. When you send coins, the protocol allows you to specify precisely how many coins and from which inputs. The client generally handles this automatically, but it really should not be hard to implement a feature in which you isolate certain inputs (i.e. ones the user feels are tainted) and either don't use those coins at all or only use those coins (to return to sender, the original owner, or wherever.) Fine grained control over your own money. The end of Bitcoin according to some.
Edit: And besides you should be using a hot wallet and an offline wallet anyway, for security. Eto's
Armory client makes this exceptionally easy
This
could work, but I think the implementational challenges are likely insurmountable. Getting the network effect of the majority of Bitcoin users all adopting the same (centralized) "taint list" seems immensely difficult.
Look at the whole p2sh controversy at the beginning of the year which is still not resolved.
Until the protocol you suggest is almost universally adopted, many people will be unaware of which coins are tainted. If 10% of the bitcoins people are holding become worthless, it would be as destructive to Bitcoin as splitting the blockchain.
I guess what I am trying to say is: if you can actually drum up the support needed to get everyone convinced of this plan, great work. But until there is some sort of consensus, so many innocent naive users will be hurt that a "taint" system will be more destructive to Bitcoin than the thefts are.
P2sh is a perfect example of what the 'community' is capable of. Fortunately one does not need to start with >50% to make this happen. Start small and then there will be a snowball effect. Although if Gox fully implements it, it will be more like an avalanche. Hmmm, I wonder if they might not want to help fund the development for the first taint capable client.
I imagine there will be a niche market for services to provide reasonably accurate data regarding thefts and transactions. The ones doing a good job will largely agree with each other, and the market will take care of those that are inacccurate/unreliable. I also imagine that there will be some kind of feedback loop for those who can prove certain coins are wrongly tainted. I have no intention of running such a service, so that's just a rough sketch. The market can figure out the details
I doubt all of the stolen coins add up to 10%, and even if they did they are not all circulating. But let's say that is 10%. Tainting them makes the rest of everyone else's coins that much more valuable. There will be some upheavals in the marketplace as things get sorted, but once the dust settles we will be left with the only currency in the world that has completely taken the profit motive out of theft. And that will bring far more widespread adoption than making byzantine security solutions that are difficult to impossible for normal users to implement.
Curious thought I just had: what if only thefts going forward were tainted? Amnesty if you will.