I forgot, maybe I should also say that there might be risks in using public mixers, depending on the legislature you're under.
Let's suppose you use a mixer, doesn't matter for what. The idea of a mixer is that your coins will be used by somebody else, and somebody else's coins will be used by you. If this somebody does something nasty and the trace is being followed somehow, it could end up on your wallet or exchange account. People could end up reaching you instead of their original target. And if you say "that's not me, I was using an anonymizer", that by itself may bring you troubles in most jurisdictions of the world.
Honestly, if you want to be truly anonymous, avoid non-anonymous exchanges like MtGox. Even OTC is might be risky if you use bank transfers. The only safe harbor is cash, unfortunately,
Obviously you can get dirty money from a mixer, but the relevant part is that you don't get money from the same dirty source more than once maximum twice. I mean, sooner or later all money will be dirty, somewhere in the chain? That doesn't mean you can convict random people that might have owned the money at some point.
If you could break the transaction chain cash wouldn't be the only safe way. Cause it doesn't really matter if people/gov can see that you've got BitCoins that you traded for USD as long as they can't trace where the BitCoins come from. I could just say "Donations from my blog" or whatever.
Ps. It's funny that so many people talking about BitCoin just say "You can make it anonymous if you use it right/smart" but no one seems to know the right/smart solution. Or is the smart people sticking together and not sharing?
It depends on the level of anonymity you want. For most cases, just using bitcoin normally is probably anonymous enough, particularly because currently no government is crawling the blockchain, searching for victims. And when/if they start doing it, I'd expect solutions to appear. Pretty much like their "war on piracy".
Sucks for those who get in trouble after the gov start to crawl but before there are options to be anonymous. Would be nice with some proactive actions.
Though I think a lot of people want to be anonymous even though they're not doing anything illegal. That's probably the same people that think 5% for mixers is way to expensive.