This community should have a very clear answer to this questions, no one serious will invest in this Economy in the long run without a clarification and Bitcoin will just attract small players and hackers.
There is no official policy regarding "tainted" coins. Every single user of bitcoins is entitled to refuse to accept bitcoins as a payment for whatever reason, including the reason that he or she considers the coins you have to be tainted. Someone may refuse to accept your coins, and that is their right to do so.
What is relevant to your trade in bitcoins is what the policy of the exchange you plan to use is. If you plan on using Mt. Gox, ask them what their policy is on tainted coins. Not satisfied with this policy? Choose another exchange.
The concept of tainted coins seems to me to be destined to fail. Take the recent Bitcoinica theft as an example. A number of coins were sent to the "Bitcoin faucet" address. Owned and operated by lead Bitcoin developer Gavin Andresen. What now? Should we not accept Gavin's money, and all other addresses that receive money from the faucet?
If an exchange chooses a restrictive policy on tainted coins it simply means I will go exchange my coins elsewhere. I am not a thief, and I will not accept being treated as one. This dynamic will dig the grave for the concept of tainted coins I believe.