Someone from /r/bitcoin was asked to explain "the primary use case for your Coinbase account," "the source of the bitcoin being deposited," "the source of funds for your bitcoin purchases" and "the nature of your outgoing transfers and what, if any, services they are related to."
https://pay.reddit.com/r/Bitcoin/comments/2fkfe7/moved_my_bitcoins_off_coinbase_and_got_the/
This will be common sense for many of you. Remember not to make large transactions that you can't explain. Personally, I stick with LBC.
Just send your coinbase purchase to one of many cryptocurrency exchanges (BTC-e.com or cryptsy.com seems the best as they are the shadiest) solves this issue... do your own tumbling by trading BTC for any alt coin then selling back for BTC. Rinse and repeat till you are not paranoid then send to marketplace. Good luck tracking BTC blockchain to alt coin blockchain a few times... especially when the exchange is in Ukraine or Russia or somewhere like that.