I would avoid depending on the ability to upgrade. It's always a gamble and availability of parts and a guarantee of compatibility is never assured no matter what brand you get.

What are your other considerations? Size, weight, battery life? Usually not important when looking to spend that kind of money on a gaming computer aka desktop replacement.

Take a look at the Sager NP9262 equipped with two 9800m GTX SLI and a 3.0GHz Core 2 Quad. It is considerably more powerful than anything Alienware has at any price and will be cheaper too. In fact it's still the most powerful 17" notebook you can buy. There are a couple reviews in these forums but no one has benchmarked a really high end configuration as far as I know.

Another thing I like about Sager is it's not as gawdy looking as Alienware or Dell and appears more serious and business like which is important when I'm passing the time sitting in a conference room playing COD5 while customers are walking by. It's a solid and well built machine too. Another thing I like is I buy mine with no OS installed so I can configure it the way I like. Many people don't want to do this but it's a feature that advanced users like that Alienware and Dell don't offer at all (must buy Windows). Alienware used to buy their internal components from exactly the same supplier as Sager (Clevo), until Dell bought them and started putting Dell components in them. This is my second Sager and I wouldn't touch Alienware any more.