According to the American Customer Satisfaction Index, consumers are happier with their computers than ever before. The latest numbers from the group give PCs 78 out of a possible 100 points—an increase of three points over last year. Acer, Dell, and HP all scored 77, while Apple did much better with a score of 86.
This page on ACSI's website describes the group's methodology, which factors in perceived quality and value in addition to customer complaints, expectations, and loyalty. Customer loyalty is named a "critical component" of the assessment model, and I suspect its prominence helped Apple to score so highly. PC users can easily switch brands without migrating to a different operating system or losing applications. Parting ways with Apple is considerably more difficult if you want to keep running OS X.
ACSI's historical data goes back more than 10 years, and it nicely illustrates a dip in customer satisfaction during Vista's tenure. Windows 7 is credited with fueling the rebound, which seems like a fair assessment given that the OS is really the biggest change we've seen on the PC in the last year.