Very quick reply, I should be going to sleep:
I think it would be helpful to describe how much anonymity you can expect based on what you expect from a potential attacker.
There's a big difference between "I'm worried about somebody tracing transactions back to me by looking through the block chain" (easy solution: mix up your coins by sending them to and from a mybitcoin.com account a couple of times over a couple of days; send them in batches over time to be really safe) and "I'm worried about somebody tracing the transactions I'm making by watching all of the IP traffic coming from my machine (much, much harder to guard against).