I love that article by Keith. Nice choice of some of the parts that he had 'just lying around........Bontrager frame.....brazed unicrown fork......Sante rear derailleur......prototype tires....prototype rims.....prototype cranks......prototype seat......prototype.....
HAHA!
Anyhoo.
If you're not sure about the singlespeed thing, build up a cheap beater, or just don't change gears on your current bike. Simple. Or if you're hangin' out for a new frame, get a geared frame with a Bushnell EBB. Sure, it's a compromise, but it's a versatile one.
If you live in the right part of the world, a singlespeed MTB is the most versatile bike you will ever own, but don't just rush out and buy one because you heard it's cool. I'm not suggesting that's what you're doing because I don't really know - however, there's also no point in building up a bike you'll never ride, too.