From the Hitwise Press Release:
Google accounted for 68.29 percent of all U.S. searches in the four weeks ending May 31, 2008, Hitwise announced today. Yahoo! Search, MSN Search and Ask.com each received 19.95, 5.89 and 4.23 percent respectively. The remaining 41 search engines in the Hitwise Search Engine Analysis Tool accounted for 1.63 percent of U.S. searches.
So, no surprise that Google continues to dominate, growing their market dominance to 68% of all searches. Ask.com was up slightly from April. MSN and Yahoo were both down.
In the UK, the dominance was even more pronounced, with Google taking 87% of all searches!