The HXR-FMU128 normally retails for $749.95, but the $500 rebate brings it down to a much more palatable $249.95. Since 32GB SDHC cards are selling for about $100 right now, with the rebate the HXR-FMU128 comes in at almost have the price of four 32GB cards.
[UPDATE] It seems that the date for filing the rebate was extended, but the period for buying it did not change. The important details that may have caused confusion when looking at the rebate forms:
Eligible models must be ordered from a Sony Authorized Reseller, Third Party Reseller of an Authorized Distributor or directly from Sony by March 31, 2010 and shipped to end user customer by April 30, 2010 to be eligible for rebate.