$HTTP_HOST ought to just do the domain itself, explode() off the www or regex it to strip out the rubbish.
If you are building a holding page for names it is worth logging everything eg.
$date = date("l dS of F Y h:i:s A");
$ip = $_SERVER['REMOTE_ADDR'];
$browser = $HTTP_USER_AGENT;
$os = $_ENV["OS"];
$referer = $HTTP_REFERER ;
$searchterm = "FRONTPAGE";
Nice and handy to find out who is visiting site, where they have come from, what they did prior to contacting you etc etc. Logging IP's can be handy to see previous visits as well.
Others do things far more in depth than the above, but it can be very handy
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