You shouldnt trust coin mixers, be very careful with them since they can steal your bitcoins and never send them back to you while they are "mixing them"
that's true.. and that's why , when you want to use a mixer service, you should always choose a trusted and reliable service.. be extremely careful when using 
these kind of services..The problem is the type of people who set up mixers. Most I don't think are in it to help people remain unknown. They are in it to make money.
If a government shows up asking for IP logs you know they will be turning it over very very quick hoping to not spend a ton in lawyers.
Also biggest concern is they just stop sending out. Lets say business is slow, they get a big amount to mix. They run away with it and any smaller ones that were sent before people realized it.
Just a lot of possible bad things.
About IP and Goverment. There is 2 sites at BitcoinMixers.com that need no registrations. Using VPN/proxy you get your adress for sending BTC and using TOR send them and got your new bitcoins. Simple, yeah?
What makes you a expert in this field can I ask? Tor has had more holes and exploits then I have counted. As long as there is exit nodes it remains open to possible attacks.
But why do all this with mixers when mining to a new address is more anonymous?
Let me give you an example: at BitcoinMixers.com you can find Helix light mixer that does not just clean your bitcoins it gives you brand new freshly mined uncirculated bitcoins. The Helix's system is more than a simple bitcoin tumbler, it is privacy and security wrapped in one.
