You can certainly be fully anonymous with bitcoin but care must be taken... Mainly, you need to isolate your change to an identity wallet - a wallet used for specific purpose under a dedicated pseudonym. Identity of the pseudonym is protected by plausible deniability - "I bought those coins on MTGOX, but I sold some of them to some guy for cash on the street corner, that purchase wasn't me"

The more hops through a wallet (which can be created dozens of times), adds more plausible deniability and separation to any purchase.