The Wall Street Journal reports that Nasdaq will drop Apple's profile in its Nasdaq-100 stock index, lowering Apple's share from 20.5% to around 12.3%, more in line with the number of actual Apple shares out there. Apple is one of 81 companies who are seeing their shares lowered by the rebalance, while 19 other companies, including Google and Microsoft, will have their shares increased. The index was last adjusted in this way back in 1998, but back then Apple obviously wasn't nearly as big a company financially as it is now, so Nasdaq is simply adjusting things to bring shares more in line with the actual market.
The changes should take effect on May 2, and Nasdaq does