2. Misconception. You can run a ATI card on a nvidia chipset mobo and vice versa. The only exception is if you do crossfire or sli, then you need a supporting chipset. X58 does both CF & SLI. Only premium P55 does both. And AMD chipsets do CF & nVidia chipsets do SLI. Make sense?
3. Only i7 860 is LGA 1156. Don't listen to anyone. Check it out at intel.com. If you want to blame, blame the confusion on Intel. They decided on i3, i5, i7 & i9. And they threw in i7 860 for LGA 1156. AMD, on the other hand, is more focused on 1 and only: AM3.
1. There are other good brands besides Asus. MSI is good, as is Gigabyte. Those are my favorite 3, though there are other brands people like. I like DFI, too.
2. As said, only have to pair up the chipset and video card if you're going to SLI or Crossfire. Of course, your CPU choice will decide which chipset you need, too.
3. i7 is either the 1366 (like the 920) or 1156 (860 series). i5 and i3 are 1156. i7's on the 1366 are considered top-of-the-line and I believe the forthcoming Gulftown chip will be on 1366. There are differences with the 1156 chips, especially the intergrated PCIe. Performance-wise, things are close. Intel looks to be supporting both sockets for awhile. Tom's has several articles discussing the various chips...read those for good info.
4. i5's are good, depending on what you want to do. Read some Tom's reviews on them. Check out any benchmarking articles to get an idea how they perform in various tasks.
As you can see, opinions on motherboard brands vary. MSI has been good to me and plenty other people, as has Asus. I've had issues with Gigabyte, but it's a good brand-all the big names will have occasional issues.
Stick with ASUS or Gigabyte, cant really go wrong there.
1156 socket is mainstream (i7 8xx and i5 7xx), your 1366 socket is high end (i7 9xx)
Chipset selection isnt going to matter unless your going SLI/Crossfire
p55ibexpeak - AMD f'd people around with Socket 940, 939, 754 and now we have AM2, AM2+ and AM3 - dont tell me AMD is any better.
yeah 754/939/940 screwed people over, though the AM2->AM2+->AM3 was a socket progression not like having a mainstream and enthusiast socket, also keep in mind that there is backwards compatibility (even if the motherboard makers didn't give updates for it)