A few of you have reported problems with the template chooser plugin in the past, where new selected templates would only show their true design after you've manually refreshed the page (F5 in most browsers).
The root of this problem was that browser cached the CSS stylesheet on their own, without making HTTP requests to check for changes. Since serendipity uses URL rewriting to achieve pretty URLs for stylesheets, this interfered with the one-time caching of stylesheets, even though their contents changed.
As a workaround, I've just committed a fix to our repository of the nightlies and an upcoming 0.9.2 maintenance release. This change makes the plugin always use a URL that contains the name of the stylesheet, and thus works around the caching issue by emitting individual stylesheets.