Initially, it was thought the probblem was memory compatibility..then someone said it was the PS. I notice some power supplies have the addenda "Compatible with Core i7 Power Supply". Is this absolutely necessary? (I have a Coolmax 950W PS lying around, bought 1 year ago, which doesn't have this designation)
Like you, I can't find a description of any extra specificaton that must be met so its "compatible with i7".
Some Gigabyte mobos have reported boot loop issues - my personal understanding is that it is caused by the mobo trying to load the last good CMOS configuration and rebooting itself to recover. Tweaktown forums (home of Gigabyte tech support) normally clears these problems with a rigorous CMOS clearing (ie, use all techniques to ensure it is cleared).
If your psu still delivers enough clean power within the ATX spec, it should work fine.
it all depends on how much more then just the motherboard and cpu...starting at 550 watts and up
like kg said, 550 should be a baseline. Your graphics card/s and whether or not you will be overclocking your system will determine how many more watts you'll need. Also look at the distribution of the 12 rails, try to get one with a single rail or a few (the ones with 4 or more are usually not distributed that well).
The "certified for core i7" labels are just marketing, they really don't mean much at all. That label doesn't ensure that the psu is great, it could still be mediocre.