This is a tactic that folks within Microsoft have been using. Sean Alexander wrote about it in his blog… basically it uses a web services watching piece of software.
Average time I’ve seen for sporadic Xbox 360 availability is about 4-20 minutes before sell-out over the past few days. This means you need to get notified down to the minute. So I wrote a how-to that combines an free web inventory tracker with a freely downloadable shareware app to play a chime when the tracker status is updated with new availability:
Target.com, CircuitCity.com and WalMart.com are all getting bundles and console shipments in multiple times a day for online purchase.
kurtsh
Kurt Shintaku's Blog 