Yes, Apple is fourth in worldwide marketshare behind Dell, HP, and Lenovo
according to Gartner. Same is true for the US region, but Apple has nearly twice the market share it has worldwide. In both worldwide and US, Apple is showing more growth than any other manufacturer.
None of that, however, should cause anyone to worry about the Windows laptop market. Apple's MacBook business is obviously very successful, but HP, Dell, and Lenovo have cheaper options and that is always going to drive higher market share. It would be interesting to see what the market share is for laptop at the $1000 and higher price point.