Regardless of whether HP or Lenovo is in the top spot, it's a tough race and one that HP is struggling with.

"On Lenovo's side, things must be pretty sweet," said Charles King, an analyst with Pund-IT. "It wasn't that long ago that people were dismissing the company as a lightweight wannabe." King adds: "Proving detractors wrong is satisfying but to maintain its new leadership position the company will have to keep on with what it has been doing -- blending solid value with innovative new design points."

Gartner noted that Lenovo was smart to take an aggressive position on pricing, especially in the professional market. That helped the company achieve big market share gains over the last two years, exceeding regional average growth rates across all regions.

As for HP, slipping out of the top spot may sting but it's not devastating, King said.

"It's a bigger deal symbolically than in any business sense," he said. "HP has been on top for so long that some will consider this a major disaster. But let's face it, PCs are HP's lowest margin business so while any reduction of share is somewhat painful, it isn't the end of the world."