No doubt you will have by now heard of the movement called Occupy Wall Street. Their website can be found here http://occupywallst.org/ Although they have a pretty loudish sort of rhetoric and have even been likened to the "left's version of the Tea Party", I think that just like the Tea Party, the whole Occupy Wall Street movement will prove to be a poor player that struts and frets his hour upon the stage and will be heard no more; full of sound and fury, signifying nothing.
Duverger's Law suggests that in a plurality voting system, over time it should produce a tendency towards two-party politics (This makes for interesting reading). Really the only way to upset the system is to form a new party with sufficient clout to upend one of the existing two.
Especially in the United States where there is no direct opposition to the President in the mechanics of government (because he doesn't sit in the congress), it means that the job itself will only be a revolving door between two parties.
Small groups like the Tea Party and Occupy Wall Street although they might help to colour the political discussion and may on odd occasions might see their ideas adopted by the exiting two majors, never can do much beyond that unless there is a seismic shift in the political landscape. The Lib Dems in the UK could have done that if Clegg hadn't been such an ultimately weak leader; in practice in the short term they'll occupy the same niche as the National Party does in Australian politics over the next few election cycles.
Currently in the US House of Representatives and the Senate there are ZERO "third" voices. Third Parties do exist but they contribute virtually to political discussion without solid representation because they don't have voices on the floors of houses.
Seemingly the American Public even if they complain, are through their current voting actions fine with this. If they weren't they'd do something concrete.
Certainly the consequences of Duverger's Law and two-party politics is quite an adequate explanation as to why it's so rare for someone who isn't a Republican or a Democrat to be voted to the Congress, or why there hasn't been anyone but a Republican or a Democrat who has been voted into the Presidency since possibly Johnson.
The deck is currently stacked in favour of the existing two and the party machines and the rather drawn out process of the primaries more or less ensures that the status quo is maintained. I can't forsee anyone but a Republican or a Democrat taking up either the Presidency or a seat in the Congress for a very very long time.
That's why I don't see groups like Occupy or the Tea Party having very much influence at all. It's putting people into seats that actually changes real policy in the long run; since it isn't likely in the short term, I fear that the movement is futile.