Congratulations on your choice! I don't know the XPS series that well but I know that Dell make very, very nice machines. I want to buy a new machine somewhere next year and Dell is definitely included in the options to consider. But, obviously, I'm also considering other options, like the new HP Blackbird, maybe an Alienware Area 51 but I'm also playing with the idea of building a machine again ... which also sounds very appealing to me.
My experience with Dell is very good; I never had an issue with my machine on that level. The issues that I had were all software related and I have myself to blame for that

See my signature for my specs; but keep in mind that this baby is nearly four years old! I bought this machine in January 2004 and I am still very satisfied with it. It came with 1 GB of RAMand an ATI Radeon 9800 Pro which was considered a high-end ($500) card back then. Over the years I've upgraded several components (like the Raptor 10K drive, the Gainward card, a Zalmann cooler and more RAM) to keep up with the latest (Flight Sim) developments but I am sure it can compete with some newer systems people may have in these forums. Now I must add to this, that Nick Needham and Michael Greenblatt (FS-GS) has some serious influence on that too.
The only minor drawback that I find is that their BIOS is very limited in overclocking functionality. But I never needed that anyways. So in my opinion with a Dell you have a very good and stable machine and an XPS will definitely deliver!
Let us know when you get it and how it performs