znort987, you have assumed a fact not in evidence which is 'ownership of bitcoins'. I suppose it depends on what the definition of is is.
Nevertheless, I think znort987 is raising some very good issues about how one should prepare for future interactions with the police state. I highly recommend people watch BUSTED: A Citizen's Guide To Police Encounters. If you have a police encounter in a foreign country then demand to speak with an attorney and the embassy for the passport you entered the country on.
I think the anonymity and fungibility issues znort987 is raising are important although not necessarily imminent. There is a lot of value to severing the audit trail and sending an investigator on a wild goose chase. This is what the mixing services do. Think of all the time and resources it takes chasing down bad leads. If Bitcoin does anything well then it would be creating thousands and thousands of bad leads, a true force multiplier. Sure, an investigator can chase down a crook but there are going to be a tremendous amount of completely innocent people he has to weed through while trying to accurately identify the crook. Even the State's resources are scare and will therefore be allocated to the highest priority targets. So, don't be one of those targets! Nevertheless, in this way Bitcoin can create plausible deniability.
For example, have a laptop you bought with cash with full disk encryption, have a TrueCrypt volume with a hidden partition and within the hidden partition have your Bitcoin application. Then wear a hoodie and sunglasses while you connect to the Internet from a public WIFI network with TOR outside the vision of any cameras. Then open the TrueCrypt volume and transact via Bitcoin. When finished close the volume and power down the laptop. To create even more circumstantial evidence in your favor have your alibi take your cell phone, which uses Silent Circle, for a walk on the beach.
It is going to be extremely difficult to prove to the standard required for a criminal conviction that any particular person was the person that initiated the transaction.