Update: This issue will no longer exist once WordPress 3.3 is released: http://core.trac.wordpress.org/changeset/18541/
I just learned today that certain permalink structures in WordPress are better than others from a performance stand point. As it turns out, starting the permalink structure with %postname%, %category%, %tag%, or %author% can cause a performance hit on blogs with lots of posts and/or pages. Now whether the performance is more important than SEO, less important than SEO, or moderately irrelevant to SEO is still up for debate. There appears to be a bit of an argument between SEO “experts” and WordPress developers/enthusiasts over what the best structure actually is. After reading Otto’s explanation of the performance issues involved, I’ve decided to change my permalink structure from:
Thankfully, WordPress recognizes this change and automatically redirects the old URLs to the new ones so no links are broken and no plugins are required.
(Update: Since my blog is quite small still, I’ve decided to switch my permalinks back to the category./postname method)