Can miners reject transactions from an address? It is alleged that the stolen Bitstamp coins are in this address. In theory, could miners agree to reject all transactions from this address? And if so, would all miners need to agree or just more than half?
Technically it is possible to blacklist addresses, and it needs just the majority of the mining power to agree.

The problem is arriving at the agreement: Nobody stands to gain from witch-hunts, so a consensus to block an address would have to be carefully built on solid proof, which is hard when there is no central organs with jurisdiction, nor a way to get a statement from the culprit.

Also, blacklisting addresses, just like tracking tainted coins, has a strong implication on what we view Bitcoin to be: One of the sources of Bitcoin's value is that bitcoins are considered fungible – that each individual does not need to care about the history of a bitcoin, because a bitcoin is a bitcoin. If we start treating bitcoins differently in accordance to their transaction history, it will make the bitcoin economy more complicated and less useful.