Update for Hammerhead here. My son's XPS arrived yesterday, so although this is apples and oranges, here is a comparison of my experience so far.
Delivery - ordered the XPS last Saturday, it arrived Friday, a few days ahead of schedule. On my Ozma M (5500), scheduled delivery time was two months arrived a month early. No clear winner here.
Dead Pixels - none on the XPS, the 5500 had one, it is outside the center, but within Alienware policy. With a dark background it is annoying, but I knew the rules. I talked to 2 of the 3 people at work yesterday who own an XPS, and they also have 0 dead pixels.
Configuration - configuration on the XPS appears to be exactly as ordered, the Alienware was incorrect (5400 RPM drive was secondary drive, 7200 RPM drive as the primary, this was backwards, although I did change my order mid flight, but still no real excude and this could have been caught if they emailed an updated configuration).
Crapware - I hate all the extra software they install on these things, Alienware a clear winner here. Only extra software I ordered was Norton security stuff on both machines, the Dell was loaded with stuff I uninstalled.
Problems out of the box - none on the XPS so far. My 5500 would not play games correctly. I spent a week reseating the graphics card, trying different drivers, and finally after one reseating of the card, games worked correctly for about an hour. Blew out the connectors on the graphics card with compressed air and it has worked fine since then. Mine came with the 5700 card, a friend said the 9700 card would do a little better for gaming, so I should be getting the new card today (two and half weeks later than promised delivery). I know this will be an incremental improvement, but what the heck, I didn't intend this as a gaming machine, but I have picked up a couple of racing games for fun. BTW - I posted about my video problems on the Alienware forum and there were 0 repsonses from Alienware representatives.
Wireless 802.11g internal cards - range and reception seems much better on the XPS.
Gaming - since I bought the 5500 for an audio notebook and it is not available with a decent graphices card, the XPS is much better. We tried Doom3 last night on the XPS at highest settings and it looked gorgeous. In defence of the 5500, it looks very good at the slightly lower settings and plays doom3 pretty well.
Configuration possibilities - this is where Alienware really shines. I ordered my 5500 with a secondary hard drive and swappable DVD CD burner. The 7700 is very cool because you can have 2 hard drives and 2 optical drives, and I'm sure the RAID configurations must be attractive to gamers. My next audio laptop will be something like the 7700, cause I am tired of swapping the hard drive with the optical drive after a session to burn a CD. I won't have it configured as RAID, but I need a second hard drive dedicated to audio data, primary for operating system.
Cosmetics - I must admit, the blinking Alien eyes and Conspiracy Blue case beat the Skullz thing hands down.
I thnk if I was buying just a gaming laptop for myself at this point, I would go with the XPS given what I have seen. I can't compare customer support, because I have had no need so far on the XPS, I have 0 confidence in Alienware customer support, so the jury is still out.
I'm sort of wishing Dell made a really big-ass laptop like the 7700 that would take multiple hard drives and optical drives, because once bigger 7200 RPM 2.5" drives come out, I would order it in a heartbeat given what I have seen today. From what I am hearing about bigger 7200 RPM drives, I probably have a few months to see what is coming out and comparing my Dell and Alienware experiences, so it will be interesting to see what happens.
On another note, I did a little experiment on the Alienware site downloading a driver package the other night, and the best I could do as far as speed was 20KB. I then tried another website and was getting 80KB, so I wish they would take care of that. Sorry, with fast internet connections these days, I don't have the patience anymore.