Something like the below query should do the trick...
SELECT text, count(text) as SearchCount GROUP BY text ORDER BY SearchCount DESC
(Of course, this won't account for misspellings or word conjugations such as house and houses. If one user enters caterpiller and another enters caterpillar, they will both be counted once, even though it's pretty obvious they both wanted the same search results. This kind of thing is hard, if not impossible, to account for though.)