Online competitive intelligence service Hitwise yesterday released the latest U.S. search statistics for April 2008. It announced that Google hit an all-time high, accounting for 67.90% of all U.S. searches. This marks a 0.65% increase over March this year and a 2.64% increase over April 2007.

Microsoft and Yahoo, on the other hand, hit new lows: Microsoft’s MSN search engine accounted for only 6.26% (down 1.51% since April 2007), Yahoo for 20.28% (down 0.45%) of all U.S. searches. Ask.com ranks fourth with 4.17% (up from 3.69% one year ago).

Since monthly statistics can vary significantly for several reasons, I find the yearly stats far more interesting and relevant when it comes to comparing past to present. One also has to note that Hitwise only included AOL among the “other” search engines, which accounted for the remaining 1.39% in searches. I don’t know AOL’s real share, but this looks a bit low to me. Still, an overall trend should be obvious, namely that Google has continued to grow and both Microsoft and Yahoo saw their share in web searches decline in the United States throughout the last 12 months.

Now that Carl Icahn decided to start a proxy battle with Yahoo in order to unseat the company’s board of directors and to possibly go back to Microsoft to sell Yahoo for $33 a share, we’re still waiting for Microsoft’s response to Icahn’s decision. The search stats above make it apparent, however, that MSFT and YHOO both could profit from a cooperation in web search and online ads.