Mixers are really not needed anymore. If you want to mix your coins, simply register with any exchange, send your coins to them, create a new wallet, and withdraw your coins from the exchange to that wallet. Bam! Your coins are now untraceable.
Unless your exchange knows who you are. Then authorities could pressure the exchange into giving them records of your transactions.
That's right. Your coins become mixed on exchange addresses in the way that some other anonymous person will not know who you are but the authorities will.
Say you have a number of incomes like a bitcoin forum campaign, altcoin bounty campaigns, gambling. You don't want other parties to know that you're gambling, selling nudes for bitcoin, bounty hunting, so you move all that money through a number of addresses on the same exchange under one account.
That won't help you when it comes to taxes though, while a mixer will.