Yeah, it took a while to get this one out the door. First, we had to swap-out the M6400 because the pre-production unit they sent us was flaky as hell.It had the LED display and the slot-load drive, both of which were buggy (DVD drive would hang the system from time to time while the LED display would get confused about when to turn-on the back lighting after a resume). The replacement had the normal LG D4C01 matte display and the tray-load DVD-ROM (no R/W!), but at least it was stable. Typing from that unit as we speak. :-)
Then there was the HP. Initially, they shipped it to us with only 4GB. Worse still, the unit had some bizarre pre-production/prototype quad-core chip (2.4GHz????). It took them a month to realize what they had done (we kept telling them that none of the normal utilities could recognize the CPU), and by then I was already overseas. Took 3 weeks to ship the unit to Houston, swap it out for a production-level config, and ship it back to me (I'm on Mauritius, an island in the Indian Ocean, and customs here is hell to deal with).
So, basically, it's a miracle the review ever got finished. As for the display comparison, I've seen both types on the Dell - and the HP has the "DreamColor" - and, frankly, I can't tell the difference during day-to-day use. The LED units certainly look "brighter" - the colors sort of "jump out at you." However, unless you're really into digital image/video editing and need that full-range Adobe color support, it might not be worth the extra $$$. Also, that edge-to-edge glass business on the M6400 is great until you start to smudge-it-up. In fact, the whole unit is rather smudge prone, something I mentioned in the review (keyboard and palm rest turn into an oil slick rather quickly during heavy use).
One thing I can say for certain: This thing is FAST! In fact, it's the fastest client system of any type I've every used. The 8GB is heaven for a hard core VMware user like me (heavy development/testing of large n-tier web apps), and the RAID 0 makes snapshotting and copying VM images around a breeze. Easily twice as fast as a single-disk rig, and with the M6400, I don't have to dump my optical drive to reap the benefit. Nice.
Bottom Line: Dell will have to pry this eval unit from my cold, dead hands... :-)