Many users note that Apple's 5GB iPod supplies are absent. According to Apple, the reason is due to high holiday demand.
Others are speculating that this may indicate future updates... but supply and order-lead-time speculation tends to be terribly inaccurate.
However, MacWhispers notes that according to their sources inside Texas Instruments, they are shipping new low-power Firewire 800 interfaces to Apple -- hinting at future iPod updates.