A Tobin tax on capital/flows/currency exchanges  as well as onshares/cdos etc. purchases would have the effect of dampening such huge speculative flows whilst not ultimately restricting real long term investments made on rational grounds.  

A Tobin tax is impracticable in a global clearing system with consolidated clearing,layers of intermediaries, and disparate jurisdictions which regard lax regulation as a competitive advantage.

In a decentralised networked clearing system, within a suitable global framework, on the other hand, it's a no-brainer.

"The future is already here -- it's just not very evenly distributed" William Gibson