The over use of WordPress plugins can make a site slow to a crawl, Kim Castleberry, writing on Business2community.com has posted an interesting article “How To Find Out Which WordPress Plugins Are Making Your Site Slow”
“Google, with their emphasis on Site Speed and loading times, has made it clear to website owners that slow sites will not be tolerated!
While it’s very challenging for a WordPress blog to hit (or be under) the preferred 2 second mark, unless it’s only running a theme and no plugins… by the time we layer on some fancy-dancy plugins these sites can get downright slow!”
The article mentions P3 (Plugin Performance Profiler) For WordPress, a performance scanner for WP.org blogs and details some plugins performance.
Dev4Press (author of the GD series of plugins) published a set of charts showing the load times of 35 WordPress plugins Visit chart