i was going to make a criticism only to find you
had included what i was thinking of further down the page.
a couple of things of note:
it's good to take a reading during POST and powerup because HDDs draw a lot more current when spinning up. so you want to know how far, if at all your rails drop during spin up as an upgrade may mean it drops too far to power up
i like taking readings while running F@H (or prime95) on both cores and 3Dmark at the same time. that way you can be certain your cpu and graphics systems are at full load.
good guide, i want to sticky it but if you've noticed the hardware pages are all getting a bit cramped with stickys (especially overclocking). i'll see if i can do some shuffling to make it fit.
remember pretty much all PSUs these days have multiple rails that run virtually independant of each other, you may want to include something about how to measure each 12v rail. the first 12v rail to my understanding is always through the ATX connector. the second rail will be through the molexes (i think) and definitely the PCI-E connectors, at least in a two rail system. i'm not sure how it goes from there but you should be able to look it up.
edit: going to give it a try in the hardware troubleshooting forum.