Shares of Apple hit $600 for the first time, boosting the computer and electronics developer’s market capitalization above $560 billion. REUTERS

Shares of Apple (Nasdaq: AAPL) rose slightly after an early plunge Friday as sales of its latest iPad brought lines to its U.S. retail stores and wireless company outlets.

After a two hours of trading, shares rose 29 cents to $585.85 after they fell as much as $6 at the open. On Thursday, the shares of te technology giant set an all-time record of $600.01 only a month after breaking through $500.

Despite the fall, the Cupertino, Calif. company remains the world's most valuable, with a market capitalization of $540.7 billion.

Apple has said the new iPad is sold out in the U.S. and several other countries. It's sold 55 million iPads and iPad2s over the past two years. One estimate, from Yankee Group, is that as many as 2.5 million iPads will be sold within the next three days.

The new iPad will be available next Friday in 23 more countries. Friday's rollout included the U.S., Canada, Australia, France, Germany, Hong Kong, Japan, Singapore, Switzerland and the UK.

Analysts have questioned whether the share price could continue indefinitely on its rise. So far this year, Apple shares are up 43 percent. Two more analysts raised price targets for Apple on Friday. Oppenheimer's Itai Kidron set a price of $700 while Maynard Um of UBS published a new target of $675.

Earlier this week, four analysts raised their price targets on Apple shares, with the highest target being $960, published Wednesday by Morgan Stanley's Katy Huberty.

Separately, Andy Kessler, a former Wall Street analyst, published a skeptical column about Apple's prospects in the Wall Street Journal, which questioned whether the shares had risen too quickly too fast. Momentum works in both directions, Kessler wrote. Pull of up the charts for General Motors (NYSE: GM), Xeros (NYSE: XRX) or Eastman Kodak (Pink: EKDKQ) on your iPhone.