Build or buy? Bang for your buck:custom job vs Alienware X51?

Hey all. I want to get an awesome gaming PC that I'll also be using as an HTPC. I usually build my computers because I find it is cheaper, I get what I want, and I enjoy it, BUT price wise I'm finding it difficult to want to go down that path when there are systems out there like the Alienware X51. At $700 it seems like a great deal and a nice looking rig.

What do you all think? Build or buy?