I think Alienware are the Oakley of computers. They sell a name, not a product.
A home built computer of the same specs can be made for a significantly lower price than the Alienware. It will perform the same, and with the money you save you could buy better components and make it perform BETTER. And as earlier threads have pointed out, you can find cases just as cool. In fact, years ago when Alienware used their black hydraulic case, I bought the exact same one on Newegg. The only difference was mine didn't have a microscopic Alien head sticker. Building your computer is incredibly simple, and if you want pure customization, there you have it. Some would argue the new cases are tacky (me included) but that's personal preference.
Like it has been said, individual parts carry the same, if not better, warranty as the Alienware.
Tech Support is available for specific components in a home-built machine, and generally if you have -some- computer and internet searching skills, you can fix most problems on your own.
I personally don't want to spend $500-700 for a name. And a sticker. Well, you get the T-Shirt too....
Alienware is a marvel of marketing. With their futuristic site design, and impressive cases, and self-touted title of king of custom computers, it's easy to believe you are buying more than just a computer. It seems like a community, like you are buying something that sets you apart. I fell into the marketing trap, and I'm sure glad I climbed out.
To me, Alienware is hype.