The answer is it depends.  See FAR 16.505(b)(3) Pricing Orders where it states, "If the contract did not establish the price for the supply or service, the contracting officer must establish prices for each order using the policies and methods in Subpart 15.4."  If the task order is for a particular project which was NOT previously priced/negotiated when the initial IDIQ was awarded and payment is based on completion and government acceptance of the results of that project (say a prototype), then certified cost or pricing data would be required for the task order (assuming it is over the threshold and none of the exceptions apply).  In effect, this situation would require the task order to be treated like a mini-contract for a new, stand-alone requirement even though a certification was obtained for the rates in the initial IDIQ contract.  If the task order is only buying hours and the rates were already certified and included in the initial IDIQ contract, then certified cost or pricing data should not be necessary for the individual task order.  There's a good discussion thread on this topic in the WIFCON Forums and Blogs entitled, "Is Certificate of current Cost and Pricing required for Task Orders?"