I'm currently building my first fixie and fishing around for some deals. About the cranksets, does it really matter? I've seen sugino 75s on some people's bikes, and they cost around $200+, whereas the 'Bulletproof' crank cost around $40 (w/o Chainring). As a newbie, I don't think I want to drop that much money on something like the Sugino 75. And if it really does make a difference, then I might even consider Sugino RD. I am not going to compete in any races, I'm just building for road use (commuting).
...same thing with seatpost. They're just seatpost! I know carbon shaves the weight a bit and dampens the bumps, but honest, that's what the saddle is for.