its because your using search.php to perform a more intensive request and then repeatedly reloading it. Problem is if i remove the limit, cpu cycles increase and the search can be flooded. When say google are trawling through the site, they show no regard for server limitations.
I'm surprised more people don't do it, but why not switch to a tabable browser? Middle-click opens in a new tab. Lot easier to browse forums if you keep the index open and middle click the child threads. Should speed up your browsing considerably, but its a little new if your an ie browser. Once you tab you can't go back