When changing permalinks in WordPress from an old format to a new, you risk losing Google page rank.
On my blog, I’ve had my permalink set to /archives/year/month/day/name-of-article. Looking at my web server log, very few used the archives sidebar, so I removed it. To make the link shorter I needed to remove everything except the article name. But when changing the permalink, all the incoming links will get a 404 error from all old connections, and the search result from Google, lowering your Google ranking. Not good.