There is another problem with trying to anonymize Bitcoin, I was reading
this thread and it became clear, not only you have to
trust the mixer but you'll have to worry that your coins could become "tainted" and in the future someone could wrongly acuse you of things because of your "transaction history"...
Mixing occurs naturally in exchanges and everywhere else, so anyone with tainted funds will always have plausible deniability. Of course, plausible deniability may not be much of a comfort when you are in handcuffed in an interrogation room.
Not sure to agree with the usage of the term "always" here. If you - out of badluck - bought your coins or sold some from/to somebody that get busted because he used SR often enough, good luck. You may believe you have nothing to fear because you paid all taxes and never did anything illegal, but beware of retroactive laws.
The sole fact that a link exists between you and activities under prosecution demonstrates the relatively weak bitcoin fungibility. (much weaker than cash).
If a bitcoin supporter (I am of course one btw) is being blind to this weak fungibility by design, just ask him why mixers even exist.
If I were doing anything illegal, I wouldn't put my future in the hand of a mixing service, knowing it would have to fight against (i) information outside the bitcoin system, whith which, in the grand picture you can correlate blockchain information much more than you believe when considering information available *only to you* ; and (ii) with all machine learning techniques that will be developped forever, or at least during your life time.
EDIT: The only way to not fear the last two points is to rely on systems that have mathematically provable anonymity (based on few "axioms" which anyway are keys to pretty much everything we do with encryption). I know only one such system that is both usable and not a plain scam. Besides it has a pretty nice community
EDIT 2: It makes me think of this:
http://www.spiegel.de/international/germany/puzzling-together-the-past-new-computer-program-to-reassemble-shredded-stasi-files-a-482136.htmlThe parallel is obvious to me: at the time people were shredding the secret documents, they had no clue somebody in the future would have methods, and patience, to reassemble the documents.