Whether or not Bitcoin mixing services will ever be very useful to the Bitcoin ecosystem, remains to be seen for now. Digital currency was never intended to be anonymous, and any service claiming to provide something else requires users to put their funds and faith into the hands of a third party. Plus, users have to rely on Tor to access certain Bitcoin mixing services, which only makes the whole process even more complicated. Not to mention how there is always a risk of losing funds.
http://bitcoinist.net/bitcoin-mixing-services-were-never-meant-to-be-a-part-of-digital-currency/