My highest traffic Wordpress was starting to bug down my server to a halt, and Pingdom showed my average pageload times at 1200ms. Google is putting some weight in pageload times as well now so I felt I had to do something about this.
My first step was to upgrade my server. I had my hosting company put in a SSD drive($75 a month) for my MYsql databases which That took down pageload times around 150-200ms on average according to Pingdom.
I was still not happy with the results so I started doing some research and found a plugin for Firefox called Firebug - https://addons.mozilla.org/en-US/firefox/addon/1843/ which I installed. This plugin will show you what takes time on your website so you can optimize it.
Firebug showed me 3 interesting issues.
1: some spam company had their claws in me and my local machine here which got me sidetracked a bit until I had Ghostery installed on Firefox as well to blockthat crap.
2: Back to my site - I discovered that Contactform7 - WordPress › Contact Form 7 - WordPress Plugins - even though only used on one page on the site, the contact me page, would load 3 elements on EVERY PAGE! - Solution - Plugin disabled
3: I also discovered the Dean's FCKeditor - WordPress › Dean's FCKEditor For WordPress - WordPress Plugins - would ALSO load stuff on regular content pages even though I only use that in the publishing area - solution - Plugin disabled.
I then left this sitting alone for a while to let Pingdom gather some data and I am happy to report my average pageload times are now 600-700ms which is almost half of and far more acceptable than 1000-1200ms.
Hindsight 20-20 I should have tried optimizing before throwing money at the problem, I might have been able to reach a satisfying pageload speed without the extra expense of $75 a month($900 a year) for an SSD drive.
Sidenote - Am I the only one thinking my hosting company is greedy letting me pay the cost price for the SSD drive in 3 months and then after that they score an extra $75 a month forever?
I ran into similar issues last year. In addition to troubleshooting with Firebug and disabling laggy plugins, I started running the W3 Total Cache plugin on some of my WP sites. It adds caching and minify capabilities. It also provides CDN hooks if you want/need the redundancy, or just happen to be hardcore about increasing your load times.
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I forgot to add this also took my server load from 1.5 down to 0.7 on average
I asked one of my guys to research and find a better solution.
If he doesn't finds one I will code it - there is no way I want that plugin back loading stuff on EVERY page
Sami4u (11 October, 2010)