A recent Bloomberg Businessweek article (available here) said that "China will soon overtake the US as the world's biggest economy." However, the remarks aren't all bad when you look at the facts. The authors point to a 10.5% annual increase in GDP in China since 2001 and a 1.7% annual increase in the US in the same time period.
However, looking at the GDP per capita (remember China has A LOT more people than the US), USA is at $47,600, China is at $4,400 (according to CIA World Factbook). Even if the growth rate continues at the same rate it has for the last 10 years, it will be another 28 years before China surpasses the US when you examine the dollars this way.
The article was interesting in the comments about the approach to expenditures. It points out that the US "spends, borrows and patches," while China "saves, invests and builds." Of course the current administration likes the term "invest" and "build," so the Chinese way makes sense for these parts (and they would like to ignore the "save" part.
Overall, I like Bloomberg, but you have to read the articles carefully.