Like many others, I've been searching for an Xbox 360 Premium system since its Nov 22 launch date in the US. That night I went to the Best Buy in Bellevue at midnight just to check out the buzz at the main launch store. I had no expectation of getting hold of one then (since 50+ people had been queuing in the bitter cold since the early morning). It was fun to see the atmosphere, but I was expecting to be able to get hold of one by driving round a few out-of-the-way stores the next day.
It took me two months almost to the day to get my hands on one - far longer than I was expecting. I finally found a great Xbox 360 stock tracking tool that gave me the inside track on the Best Buy inventory, and got a notification within five minutes of the Bellevue branch getting fresh inventory on Tuesday. Fortunately I wasn't doing anything I couldn't suspend for an hour, so I raced down to the store, calling a friend en route to alert him and arriving just as they were unboxing them at the front of the store.
The tool is by a developer who goes by the rather post-modern name of Untitled. It's written using the .NET Framework 2.0 and it simply polls the Best Buy website on a scheduled interval for stores near you. If their site shows a shipment, it can alert you via email, cellphone SMS text message, a tooltip on the desktop, or a screamingly loud WAV sound effect (which made me jump right out of my seat the first time I heard it). It's a nice little app and I'd encourage you to drop the author the price of a beer using Paypal by way of a thank you if it enables you to get hold of one.
New Xbox 360 stock should be starting to come in a little more quickly now that a third manufacturer has come online, and judging by sale prices on Ebay demand is starting to slow slightly. If you're trying to get hold of one and you haven't had any success so far, install this applet, stay patient and keep your car keys handy at all times!