Apple got help from the update to its MacBook laptops to push its share of the laptop market up nearly two points in May, to 14.3 percent, a research firm said Friday.

"Whenever Apple gets a new product out, they get a nice bounce," said Stephen Baker, analyst with NPD Group. According to NPD's data, the laptop "bounce" was 14 percent month-over-month.

The May boost put Apple's laptops in fourth place, behind Hewlett Packard Toshiba, and Gateway, said Baker, and moved its combined laptop-desktop sales share from 11.6 percent in April to 13 percent last month. In retail-only, Apple showed a slightly smaller increase, from 9.6 percent to 10.8 percent.

"Everybody's notebook business grew last month, but Apple's grew a little faster than the market overall," Baker said, adding that the company's growth rate has been larger than the industry average for some time. Desktop sales, meanwhile, continued to stagnate, although there too, Apple has an advantage.

"Desktops sales are declining, but [Apple's] are declining a little less than others." Apple's desktop machines -- the all-in-one iMac, Mac mini, and Mac Pro -- accounted for 10.4 percent of all desktop sales in May, a small increase from April's 10.2 percent. Apple should get another boost starting next month, as back-to-school purchases begin, Baker said. "Apple will have a better bump at back-to-school in the July-August-September time frame. Everybody gets it the last couple of years, but Apple gets a little bit bigger one, since compared to the Windows guys, it's doing more notebooks."

Not that everything is rosy. "What we're seeing in general is that desktops have been a little weak in the first half of this year, and although notebooks have been strong, they're showing a declining rate of increase, if that makes sense," said Baker. "In 2006, even 2005, the month-over-month increases were around 50 percent. Now they're 30 percent, 35 percent, even 25 percent."

Laptop sales are hitting a couple of plateaus that even Apple won't escape, Baker argued. "ASPs [average sales prices] have flattened out, and are pretty stable now month to month. And at some point, you just can't keep growing [sales] by these numbers."

He's also predicting that this year's back-to-school sales will be less impressive than in past years. "The market is slowing up a little. I'm pretty bullish about back-to-school, but a little less bullish than I have been."

Baker also said he expects Apple will soon revamp its primary desktop line, the iMac, a move that Apple-centric bloggers predicted would happen at last week's Worldwide Developers Conference (WWDC), but are now forecasting for end of July or early August. "I would suspect [an iMac refresh] would happen pretty soon. Both of the notebooks have been updated, so now it's time for Apple to look at that piece."