The answer is that nobody really knows. Nevertheless, the effects of increased saving and/or reduced consumption on economic growth to date have been devastating. In the US, consumption took -2.75% and -2.99% from overall growth in Q3 and Q4 2008, respectively (see the BEA's contributions to GDP growth table).
The drag coming from consumption is global. Below are several regional illustrations of the average annual retail sales growth rate (per month) for 2008 and 2009 to date. Out of the 27 countries listed below, 18 posted a positive average annual growth rate in 2008, while just 5 saw the same in 2009 ytd. Note: I do not have access to "good" data for Latin America. I urge you to visit Vitoria Saddi's blog, Latin America and Brazil - On Economics and Politics; she recently wrote a nice piece summing up the expansionary monetary policy across Latin America.
Note: For each graph below, the month listed in parenthesis next to the country name indicates the latest data point for retail sales. 2008 is the average annual growth rate spanning the months January to December. 2009 is the average annual growth rate January to date.
Retail Sales in Asia: Australia and China holding on
Retail Sales in Western Europe: Ireland and Greece give the rest of Europe some perspective
Retail Sales in Emerging Europe: Latvia suffers, and Poland just barely holding on. The RGE Monitor had a nice article about Latvia and Emerging Europe not too long ago.
Retail Sales in the US and Canada: US consumers dropped off the map; both countries are showing signs of stabilization (the "not falling as quickly" story).
Looks bad - no wonder the consumer outlook is key to many economic futures.