Microsoft hardware quality
Now, don't get me wrong - this thing could well be utter pish. It could be slow, bug-ridden, feature-bereft, or just plain vapourware. And from a hardware perspective it could have its very own red-ring-o-death(tm). But...
...Microsoft have made a lot of VERY good, robust, reliable hardware over the years. One of my servers still has an original ergonomic ("Natural") keyboard from 1995. 14 years on and having been used on several workstations for 10 hours a day, 5+ days a week, for years on end, and every last key is still faultless. I've got a couple of the original first-release optical mice still going strong after all these years, too, and load of other 10+ year old bits of white/beige plastic that're still in perfect order.
Depending on who's contracted to build it, whether they go for a premium (Sony/Apple) market segment, or whether they're trying to compete at the Netbook level (Acer/Asus/MSI/etc) will more likely dictate the hardware quality than anything else. TFT screens, x86 architecture, SSDs... these are all off-the-shelf enough to have something as reliable as you want it to be - or as you can get it to be for a given price. If they start venturing into combining newer areas - large scale OLED screens, wireless charging, etc. you can see the window for hardware faults widening.
I hope it's a phenomenal bit of kit that isn't rushed out prematurely, and is built to the standards of the Zune HD... just to stop Apple from thinking that anything they release will be another golden egg purely because of the fruity logo. The market needs innovation and competition - from all players. Ideally, I'd like it to use something with a bit more grunt than an Atom based platform. Possibly something ION based would be nice?
Note: I'm no fanboy of any vendor; I just like cool new toys that make my life more fun or easier... Writing this on a Windows machine, have an iPhone to the left of me, a Hackintosh Acer Aspire 1 to the right of me, and set of Linux servers in front of me.