Notice the bolded part.

 I guess in that case the Best Buy I was at had a pretty large amount of 360's.  

In stores here there's always overstock of 360. Elites and premiums. Cores are very rare.

At least two dozens per store.

Well I went to my EBGames store near a mall in Delaware. And the cashier said that the Elite's and Premiums are sold out. I was like WHAT!!!!!

But yea the hype is true. Halo 3 is doing its thing. Expect 1.5 million copies sold in a week in America.

I haven't seen any shortage of 360s at the WalMart near me. They have like 5 Elites, and 10 Premium/Core (haven't bothered to see which, just know it's a white box).

.....At this point 1.5 Million Copies would be very poor performance for the entire week of America. Halo 3 had over 1.0 Million Preorders a month ago.

Halo 3 needs at least 2.5 Million Sales in the first Week to be considered a big success.

That said, I've noticed Xbox 360's seem a bit less in stock, but still tons to be found. I remember last Xmas, they were everywhere, walls of them.

Fixed! 

There won't be 360 shortages because they been in the market the longest and have plenty to restock which is great news for the holiday so they don't have to worry about not meeting demand.

I don't think there are shortages... I have just noticed way LESS than I have before. Again, this is all just anecdotal and is interesting what people might be seeing in their areas.

Observation today (9/22/07) around my area (we have Target, TRU, Bestbuy, Walmart and FM)

 TRU has several (6 or so) of Halo 3 360 and 4 of the Premium.  No core and Elite is also sold out

 Best Buy - 2 Premium and 1 Halo 3.  No Elite.  This is a very small Best Buy and they usually don't have a lot of stock.

 Wal-Mart - 2 Elite, 2 Premiums and 2 Halo3.  They probably have more in the back but that's what I saw in the case.  Again, no Core.

 Target - 1 Elite, 2 Halo3 and 2 Premium.

 FM (Fred Meyers) - 1 Premium.  No elite (they had one but it was sold).  They are a lot smaller than Target and Walmart so they don't really keep big stock.  They still have 20GB PS3 from Christmas ....

 So I don't see any shortage at least no in my area.  I don't really know how well they sold, but it seems there are plenty of the 360s of any Sku with exception of the Core.

 I was thinking that Halo 3 360 would be hard to find but it seems there are plenty out there.

Honestly I've seen less and less PS3s on store shelves, but that seems to be more stores simply restocking with less units than any increase in sales.