After not getting any XML sitemaps plugin to work, I disable W3TC, created Sitemaps in Yoast, confirmed the sitemaps were there by clicking an url for a sitemap.
I then enabled W3TC. The sitemaps were gone. Clicking the url that had just worked produced 'file not found.' (I'm running WP 3.4.2 w Atahualpa theme)
Any ideas about what I need to tweak?