Apple continues to grow their market share of Macs in the PC retail sales. According NPD Apple Macs account for 14% in unit sales and 25% in value of all U.S. based PC retail sales.

This numbers represent an increase of 60% and 67% respectively compared to a year ago.
Apple notebooks have seen strong sales in February. The Macbook Air might have something to do with that.
Apple still has a long way to go before they start bothering Microsoft's dominance. Slowly but surely Microsoft is loosing ground though by being attacked from two sides. Apple attacks with cool hardware paired with stylish and easy to use user interfaces. On the other front Linux comes in with low priced hardware that just does the job as well as a more expensive Windows system.
More details on Apple Insider.