If you use the Google sitemap plugin for WordPress it’s probably a good idea to disable the auto rebuild option. This is especially true if you have a large blog and a small server!
Go to Options->Sitemap and uncheck “Rebuild sitemap if you change the content of your blog”.
You can regenerate the sitemap by calling a URL with a secret key. It’s listed on the configuration page. Copy it into your bookmarks or make a cron job to call that URL at a time when your server isn’t busy. Posting to this blog would timeout quite often if the server was loaded in any way. If it wasn’t loaded before, it almost always was after! It took some time for me to figure out that it was the Sitemap generator.
The sitemap generator plugin is a great program, it does what it says on the box, but disable to the auto-update feature if you’re having problems posting!