RodeoX makes some very good points. There is NO assurance that mixing sites will always be around. But, bitmixer.io has worked many times for me, and apparently for many others here at bitcointalk.
Also that new blockchain analytical tools are "out there" which may be able to break mixing.
But, IMO, the only entity able to really crack BTC mixing would .gov. Stay out of trouble, don't break any laws (drug laws, child pron, etc.), and you should be OK.
"Smart mixing" (and other basic security) should be enough for almost anyone. Remember that spending BTC, and having something (a book or gold as examples) delivered to you will reveal you as a BTC owner to someone.
Smart mixing? To hide your trail even more, try mixing with both bitmixer.io and SharedCoin (via blockchain.info) in sequence.
I guess staying out of trouble is the best way...good point.
I will check out those sites, thanks alot!