[kh99]

I'm not any kind of expert on this but: There's a Server Configuration forum over on vbulletin.com, I believe they can help make sure you have optimal database, php, etc settings. If you have mods you could temporarily disable them and see if that makes any difference, and if it does you might want to rethink which ones you're using.

You probably realize that the "one line of code" hides a lot of work that's needed for each page, and I imagine that a lot of the time is taken up by db queries (if you put your site in debug mode you can see all the queries and how long they take). And there's the possibility of using some non-db caching to speed things up (although I'm not familiar enough with the options to suggest anything).