The new Windows Vista incorporates the Windows Genuine Advantage program(where the Microsoft website has to test your copy of Windows to make sure that you, the user, are not a dirty pirate; if the test fails, you are not allowed access to the Microsoft website or to Microsoft technical support).
Once the WGA program began, computer reviewers and average users began noticing an abnormally high failure rate in WGA tests. Inconsistencies such as reporting that a system is valid one day and, after requiring another test the next day, reporting that the same system had failed the test also began to appear.
Because Windows Vista uses the Windows Geuine Advantage program, it means that Vista must report to Microsoft that your copy of Vista is legitimate. This doesnt happen just once like it does with WGA(Windows Genuine Advantage), but rather every time you turn on Vista and connect to the Internet. Most of the time it does this silently, but occasionally it interrupts what you are doing to notify you that you have installed a pirated or counterfeit version of Vista; even if you have passed previous authentication tests.
Why this matters to you is because Vista uses this same program to determine if your copy of Vista is genuine. If the WGA program in Vista determines that your copy of Vista is pirated or otherwise counterfeit, it will reduce the functionality of Vista to the point where all the user can do is use Internet Explorer for 60 minutes per day before Vista automatically shuts itself off.
Whether Microsoft will produce a patch that fixes the poor programming of the WGA program(so that it only shuts down “genuine” pirates) is yet to be seen.
This is another reason(of the vast number of reasons expressed elsewhere) to delay your purchase of Windows Vista.