Here are my top-ten suggestions:
01) PLACE TWO MOUSE BUTTONS (you can still assign them both to left-click by default if that is such a huge concern, but after that let the customer decide what to do with them);
02) the 12'' is normally intended to be ultra-light, so place the DVD writer into a docking station or better yet - some ultra-thin external enclosure - firewire if you can provide power over it, or an "extended USB" like the Dell D/Bay for the X1;
03) remember that thin, light, cool and with long battery life are all very important things; when Intel will let you choose between a 2.4 GHz dual core 800 MHz frontbus, 1.86 GHz low-voltage and 1.4-1.6 GHz ultra-low-voltage don't be afraid to pick the lower-speed part - even if it might actually be a little more expensive the 12'' must not burn your lap and last for at least 4-5 hours;
04) be certain that people will be able to also install Windows on it - of course that SteveJ would like to have his own OS monopoly like BillG does, but for the moment that is not the case :) so instead of just being different and loosing market share this time go for "different yet most compatible" and be a winner;
05) don't be cheap on the keyboard part - and again don't be afraid to look at the keyboard from the best Latitudes or Thinkpads; since we already established that customers like compatible things also be certain that the keyboard will work great (and have all keys) in Windows; a "convertible tablet PC" might also be a VERY tempting thing, but without OSX support for it chances are rather slim ...
06) for wireless go a/b/g/n - it will probably add 5-10 US$ to a 2000 US$ fabulous notebook but buyers will love to know that it will work in any wireless configuration possible;
07) of course that the latest stuff is the greatest but it's not a bad idea to also add some of the older things - infrared, PCMCIA, even not so old stuff like Bluetooth; serial and parallel are optional on an ultra-slim but should be present on a dock;
08) if you must only have one memory slot and a default "soldered" memory don't be afraid to go for 1 GByte - RAM is rather cheap now;
09) build it TOUGH - people should not be afraid that the top lid is too thin and the keyboard will leave a mark on the screen; in case that the Nano lesson was already forgotten - SCRATCHES ARE BAD - so go for a matte/brushed finish (Latitude X200 is one of my all-time favorites);
10) last but not least - a notebook like that will certainly be among the all-time greatest but that does NOT mean that now it's the moment to add a 500% margin - so KEEP A VERY GOOD PRICE and plan to make money on volume in the long term!!!