I was a microprocessor designer at AMD for 10 years. One year they gave me a free opteron dual core processor. So I bought a thermaltake case, a massive power supply, an asus motherboard, hard drives, video card, a copy of OEM windows, a bottle of arctic silver, a heatsink, RAM, etc., and put together a system for myself.
The time it took me to pick out the parts, order them from newegg, unbox them, assemble them, test everything, update the motherboard firmware a few times, install the OS, deal with little incompatibilities between firmware and graphics card, etc., easily took a few days of my time (and, again, I'm a guy who knows what I'm doing). Figure 24 man-hours. My time is worth a lot (now that I'm an attorney, it's worth much more), but one doesn't have to come up with a big hourly rate before the "bargain" of building one's own system doesn't look so special.
Add in the fact that finished system sure ain't as pretty as the MP, and the fact that it runs Windows (huge fact right there), and to me the MP is a hell of a bargain, even at the current price/performance ratio. (And don't give me the hackintosh argument - the reason I switched to Apple is I'm done with the constant annoyance of having to hold everything together with duct tape and baling wire.)