I doubt that things will get too bad. Inflation will kick in pretty hard next year as the money works its way out of the system. That will probably cause a spike in gas prices. Other than that, it's just a retraction. We had a long period of big growth without any true "recession." People are just panicking because this is the first real time we've had to cut back.
I'm not sure what will happen with the banks. There's a lot of talk about nationalization and I'm just not sure about how that will affect the financial market and general business in the future. It will certainly be interesting.
This isn't anywhere close to the Great Depression. That had a number of serious infrastructure issues that also exacerbated the problem (Dust Bowl, crashing food prices, idiotic speculation inflating the markets, unsafe banking, a non-reactive Fed, etc.) We're closer to Japan's Lost Decade. The worst we'll see is a prolonged recession that we'll eventually kick out of.
We should get a nice recovery though. There's a lot of good ideas coming down the line that will give us a little boost in the future though.
I do think that the US will see a severe reduction in power though. I think we'll slip to a position of 2nd tier nation closer to the EU in nature of power. China will come out hard and have a serious boom (they're basically in the same spot we were after WWII).