You probably know about Microsoft's rolling deadline for stopping the sale of Windows XP. Unless you are an enterprise customer, you have probably noticed that, in North America, new PCs no longer ship with Windows XP, even as an option. So. What are the "end of" dates for the various versions of Windows?
Windows XP will receive security fixes until April 8, 2014. After that, you had better plan on migrating that old PC to linux or scrapping it. However, you are probably already noticing that some newer software is for Windows Vista or Windows 7 only; and this trend will only be getting worse as time passes.
Not that many care, but Windows Vista has already been pulled from the retail sales channel. It will no longer be an option for that new PC come October 22, 2011; and Microsoft will stop providing security fixes on April 11, 2017. While I am not aware of any applications that don't support Vista if they also support Windows 7, I suspect that hardware support may be a little trickier. Most peripherals will work with Vista if they also work with Windows 7, but you may be on your own if you run into trouble. An example is the now discontinued Dell XPS M1730 gaming notebook. While you can install Windows 7 on it, Dell will not lift a finger to help you. Keep that in mind before buying that next Dell or Alienware computer . . .
Microsoft has not released end of sale or end of support end dates for Windows 7; but, in general, we can get an idea from Microsoft's Support Lifecycle Policy FAQ:
Microsoft will offer Mainstream Support for either a minimum of 5 years from the date of a product’s general availability, or for 2 years after the successor product (N+1) is released, whichever is longer.
Microsoft will also provide Extended Support for the 5 years following Mainstream support or for 2 years after the second successor product (N+2) is released, whichever is longer.
The general availabity date for Windows 7 was October 22, 2009. So home users will no longer be able to get support from Microsoft for Windows 7 by either October 22, 2014 or two years after the release of Windows 8. Given that Windows 8 is due sometime next year, we can plan on end of technical support being no earlier than October 22, 2014 and probably no later than December 31, 2014. Security patches will flow at least through October 22, 2019. Since most of us will never ask Microsoft for support with Windows, I'm not sure that the end of technical support date means all that much, but the security patches are naturally of great importance.