$agent = $_SERVER['HTTP_USER_AGENT'];
$guri = $_SERVER['REQUEST_URI'];
$ip = $_SERVER['REMOTE_ADDR'];
$url = $_SERVER['PHP_SELF'];
if(@ereg("Google", $agent)){
@mysql_query("INSERT INTO googlebot (id, date, uri, agent, ip, url) VALUES ('', now(),'$guri', '$agent', '$ip', '$url')");
CREATE TABLE googlebot(
id INT(25) NOT NULL,
date DATETIME NOT NULL,
uri VARCHAR(255) NOT NULL,
agent VARCHAR(255) NOT NULL,
ip VARCHAR(255) NOT NULL,
url VARCHAR(255) NOT NULL,
CONSTRAINT PK PRIMARY KEY (id))
put that code, top part into a php file (preferebly index.php, and the second part is for your datbabase schema if you have one, then you can find out when and how often the googlebot hits your site.
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note: not 100% sure about the database schema as i cant test it with code already up and running on my database server, but i no the top stuff does work as it was taken wdirectly from my index.php page.