Is WGA causing legit users frustration for no reason? While Microsoft has said that WGA is more likely to let invalid software pass, according to many recent complaints it is often giving false positives. In fact, using Microsoft's own polling tools, there are many people with correct licenses and correct keys with WGA harassing them:

According to our analysis, 42% of the people who experienced problems with WGA and reported those problems to Microsoft's public forums during that period were actually running Genuine Microsoft Windows. That's not just our opinion, either. Those statistics were reported by the Redmond-approved Microsoft Genuine Advantage Diagnostic utility.
An example provided is a particular security tool that causes WGA to believe the machine is running a pirated copy of Windows, irrespective of their actual licensing. The figures listed are astonishing, with up to 42% of WGA's “hits” being actual genuine copies. While I'd like to believe it isn't that bad, the number of reports Microsoft is receiving is only going up.

Some of the problems resulting in a false positive Microsoft has admitted, such as particular flaws with the WGA software or problems with digital signatures. Others are being triggered by third-party software, which is not necessarily a fault of Microsoft. While many techies might be able to resolve the situation themselves should they be struck, there are many home users who may be even more confused.