Most share of market reports say Google has somewhere between 45 to 60 percent market share – dominant, but not terrifyingly dominant. Rich Skrenta, who has serious cred in the search world, says he believes it’s more like 70 percent. He bases this on referral information from his and other major sites (he runs Topix).
What strikes me as a potentially gating to this conclusion is that referrals to major sites does not reflect the entire web of search usage. …but it is striking nonetheless.