Windows 7 will be supported until 2020, long after existing PCs that we have today are gone.
http://windows.microsoft.com/en-us/windows/products/lifecycle
How is windows 8 going to do better multi-threaded apps? First, multi-core support has been there since Windows NT4. If anything, they had a lot of time to get this right, and I doubt that found some miraculous speed improvement just for Windows 8. Even HT processors were supported since XP.
Second, it is up to application developers to optimize application for the multi-core CPU. No OS is going to make your app multi-threaded.
Micro$oft can say what they want. Hey I hope they will support win7 till 2020! Windows 10 will probably be out by then...
I think win7 will go on life support in a few years. M$ is in it for the money... They want everyone to adapt to new OS's. Let's face it. Every piece of software that is written is going to be for windows 8. I bet you 50 bucks that DirectX 12 might be shared with windows 7, but the next major service pack will be focused on windows 8. And the next directx drivers there after will only be supported for 8. M$ wants 7 to die and you may see limited support up to 2020 but by that time no one will even remember what windows 7 was. It's been what 4 years since XP was put to rest? Can you imagine putting a copy of XP on your main rig right now? Well, just think what's gonna happen 4 years from now? When 2016 rolls around... More than likely the same thing.
I like windows 7. I think it's a cool OS and I hope you're right! I hope M$ supports it till 2022! But ya know what? I know it's not gonna happen. But on the other hand I don't have a crystal ball. I'm just looking at what happened to XP and I can tell you M$ is going to be shifting support away from 7 as fast as they can. I'm building a new PC. I have a nice copy of windows 7 but I know that if I don't spend the 40 bucks now I'm gonna have to pony up 100 bucks later and I'd rather get it over with. Even tho, I really hope Linux or some other OS maybe Google OS any open source OS leads the way one day.
It all boils down to this...
Are you going to stick with a PC and a Windows OS? Yes or No?
Are you rich enough to Afford 40 bucks? Yes or No?
Do you have an upgradable legit Windows 7 License? Yes or No?
If your answers are mostly yes, than you should bite the bullet.
If your want to hedge your bets that M$ will continue to FULLY support a dying OS for the next 8 years then go for it! Good Luck...