Natural economic forces are pushing the dollar up to encourage domestic savings and attract foreign investors. The natural forces acting here is uncertainty of the soundness of businesses.
Many businesses rely on credit to finance operations. Since credit is no longer easily available (presumably) businesses have to either show that they are generating revenues, or go bankrupt. Those businesses relying heavily on credit with little cash have to sell assets(financial, commodities etc...) to generate the cash to pay off their debt. This liquidation and asset sell off allows these assets at later point by other businesses more efficiently.
But going back to USD - massive asset sell off drives the prices down - deflationary force. When there's deflation, currency gains value because in the future it will take less dollars to buy the assets. Savers are rewarded. Spenders suffer
But now the Shiff/Paul scenario kicks in due to government/Fed intervention. Fed and the Gov't are duing everything against these forces. Fed is providing false liquidity with money created out of thin air so those businesses that rely on credit can stay alive (They should fail because they are not generating enough revenue to cover their debt). That's why Monetary base has increased so much in the last 3 weeks:
http://research.stlouisfed.org/fred2/fredgraph?chart_type=line&s[1][id]=BASE&s[1][range]=5yrs
Banks are still just sitting on this cash borrowed from the fed because they are not sure if the previous money they lend out will come back, or if people will continue to withdraw cash or close accounts. Once the banks will have a sufficient cushion of reserves they will just lend the money out like crazy again. Can you say hyperinflation?
And the government: 900billion bailout package. Financing for this will have to come from issuing more treasuries. This will have to come from dollars currently sitting idle(saved up) here at home or in foreign institutions. Other central banks holding dollars in their vaults is exchanged for treasuries and government just spends it - money supply goes up - inflation.
Our government is a spender and a borrower - so inflation is in their interest.
TLDR summary:
Free market forces is deflation and stronger dollar
Government and FED actions - inflation and weaker dollar
Edit:Credit goes to Gonegolfin for information.