Search Engine - Google Maintains Lead; Yahoo, Microsoft Gain U.S. Search Market Share

Based on the Data released by comScore, Inc. (SCOR) on Wednesday (5/11),  Google (GOOG) sites continued to lead the total core search and explicit core search markets in the U.S. in April 2011, which is far ahead of its rivals Yahoo! (YHOO) and Microsoft (MSFT). 
However, the key update here is that Google’s share of the explicit core search market declined, while Yahoo and Microsoft sites gained market share. 
How long would it take Microsoft+Yahoo to close in the gap?