Bitcoin is used as a go-between currency mostly. Though there are probably a few investors who dabble in playing this market.

Best bet is: (buy bitcoin - use multiple mixers - pay for service) or (receive bitcoin - use multiple mixers - withdraw)

It's pretty good for this purpose because of irreversible transactions.
It does raise a problem though, early adopters have too much wealth if they all start withdrawing cash the boat will instantly sink.

Perhaps someone will decide to do the right thing and recreate bitcoin to be more useful, no early adopter bias and no deflationary model to reward hoarding. That would be far more useful for what bitcoin is currently used for (go-between currency).