After the Gox dabatase leak the names and home addresses of pretty much everybody involved in BTC are now public, at least among the criminal community.

Those singing the song that goes "I don't mix my coins because I have nothing to hide" are either:

a) totally brainwashed/incredibly naive
b) just stupid.

Even if you mined the vast majority of your coins and used an exchange just to cash out a minor part of your holdings, your total BTC balance can be discovered by trivial blockchain analysis, following the links with just one deposit/withdrawal address.

Morale of the story: Everybody should ALWAYS mix their coins and use Tor for BTC related activities. Information is power. Never give it away.

EDIT FOR CLARIFICATION:

Bitcoin is pseudoanonymous: as soon as someone links one of your addresses to you (because you made a payment to him, or because a database of a service such as Gox is leaked) then he can learn your total BTC balance - or at least the total BTC balance of the wallet to which that address belongs - with trivial blockchain analysis.

By mixing your coins you make that task much more difficult, and thus you eliminate yourself from the list of easy targets in a situation as per the Gox database leak.

Said with other words: by not mixing your coins you are revealing your whole balance to the recipient of every transaction you make... And that is an important privacy breach.