I downloaded the WebServer design from http://www.xilinx.com/products/boards/s3astarter/reference_designs.htmand upgraded it from 9.1 to 10.1.
After implementation, two timing constraints fail with a big slack for setup and the memory test fails.
Adding the following constraints to the UCF can fix the problem:
NET "DDR2_DQ_pin<*>" IFD_DELAY_VALUE = 2;
NET "DDR2_DQS_pin<*>" IFD_DELAY_VALUE = 2;