I was thinking more so of people figuring out who you are and what your wealth might be via tracking the money flow down the addresses you spend with. Even if you use a new address each time, you still need to deposit on that address from another address- something that is rather trivial to track.
For this case MtGox is sufficient to mix the coins, but the knowledge about someone's financials makes that person vulnerable, and what you pointed is only one potential issue, that's why I advocate so hard for
Automatic Coin Mixing Idea,
P2P coin mixingAll you need to do is send your bitcoins to MtGox and withdraw them to a new address. MtGox processes so many bitcoin deposits and withdrawals that you've very unlikely to get the same coins back, and so nobody (other than MtGox and anyone with access to their database) would be able to tie your deposit together with your withdrawal. Alternatively, make 2 MtGox accounts, deposit into one, use a 'redeemable code' to transfer the coins to the other account, and withdraw from there. Then even MtGox can't be sure the coins didn't change hands.
P.S. Why the thread was moved to Trading Discussion?