SUMMARY: ordovician CO2 levels where thought to be 10-20x as high as we have now, while the temperatures were pretty much what they are now. the new research shows the CO2 levels were much lower, only about 5x as high. and yet the temperatures weren't higher and the earth didn't turn into a venus-like hell. for comparison, consider this:
http://wattsupwiththat.files.wordpress.com/2010/08/odrovician_co2.jpg

my thoughts:
this graph has the old 10-20x higher CO2 line. even with CO2 at 1500 ppm, it's clear that there were periods where the CO2 was low and the temperature was much higher (carboniferous) and where CO2 was high and the planet was in the ice age (end of carboniferous, ordovician). we are technically in the ice age at this point, because the "normal" temperature of earth is some 5-8'C higher than what we have now. draw your own conclusions as to what is "normal".