Here is a quote from AppleInsider today.. Since the iMac 3.06 with the ATI 4850 is being delayed at least until mid April, does it make more sense just to wait for the QuadCore and Snow Leopard release later this year? 

Read the whole article as it indicates very strong demand for the newly released products....
http://www.appleinsider.com/articles/09/03/11/apple_ups_mac_build_plans_on_strong_reception_to_new_desktops.html
"Wu, who was responsible for some of the off-base reports (1, 2) of quad-core iMacs leading up to last week's launch, says he believes Apple made the right move by sticking with Core 2 Duo processors in the refreshed line of all-in-one desktops, which "provide plenty of power" for the majority of users.
As for the first quad-core iMacs, he now says he's hearing a likely introduction in the "summer or fall time frame" to better coincide with the release of Mac OS X 10.6 Snow Leopard, which will be optimized to take advantage of systems with more than two processing cores. "
Read the whole article as it indicates very strong demand for the newly released products....
http://www.appleinsider.com/articles/09/03/11/apple_ups_mac_build_plans_on_strong_reception_to_new_desktops.html
"Wu, who was responsible for some of the off-base reports (1, 2) of quad-core iMacs leading up to last week's launch, says he believes Apple made the right move by sticking with Core 2 Duo processors in the refreshed line of all-in-one desktops, which "provide plenty of power" for the majority of users.
As for the first quad-core iMacs, he now says he's hearing a likely introduction in the "summer or fall time frame" to better coincide with the release of Mac OS X 10.6 Snow Leopard, which will be optimized to take advantage of systems with more than two processing cores. "