[Adrian Schneider]

Aside from how were coded - many will slow down your site because of what they do. Anything that is always checking for new data, or reading through lots of data will slow things down a bit.

Examples of 'checking for new data' would be
-vbpager (assuming)
-vbspy
-vbchat
-shoutboxes

things like searching can really kill large forums

Poorly coded mods can bring a large forum to its knees. Usually people forget to uses indexes, and it will have to look through the millions of posts, rather than taking a peak at the index to find something.

You won't find a mod that will track other mods' server usage. You would have to add timers to them seperately to track what they are doing and how long they are taking.