Customer fury over free upgrades regularly gets stoked. In late 2009, Dell and Hewlett-Packard PC owners went to those vendors' support sites to .

Microsoft launched Windows 7 more than two weeks before users flooded the Dell and HP forums with complaints.

That grumbling was reminiscent of an by Windows PC makers in 2007 over free or discounted upgrades for Vista.

The sluggish fulfillment by OEMs (original equipment manufacturers) of the last two Windows upgrades may have been one reason why Microsoft took control of the process this time.

At the end of May, for customers who purchase a Windows 7-powered system before Windows 8 ships on Oct. 26. Users must pay $14.99 for that upgrade, but Microsoft said it was handling everything itself.