If you're charging a 1.5% fee for this anonymous send service, how are you going to withdraw your fees? It strikes me that it'd be very easy for you to create a block of coins tainted by every coin sent through the service, which itself, should it get into wider pools of coins like instawallet, would create tainted blocks of coins that would be quite hard to send through the mixer again... Limited by the 250 depth limit, but still. Similarly anyone can use the mixer a few times to create their own "ultra-tainted" coins, aided by the fact that the mixer will always give you coins that haven't been tainted by the total sum of the taint you already possess. This doesn't even need to be very expensive if you taint a small amount of coins each time, so the 1.5% fee isn't very high, and use them to taint a much lager amount which you then send to something like instawallet.

Given how thoroughly tainted the future could be it also occurs to me that what you will eventually see is miners selling their untainted coins to the mixer, which then leads to pools inserting transactions with unusually high fees, which then leads to pools conspiring to reverse said transactions. Not to mention the question of are mining payouts tainted by the coins which lead to their fees?

Note: for all the bad connotations of the word taint, imagine how much longer and convoluted the above message would be if we had decided to call it coins' provenance.