How do I include bits of functionality only on individual entry (permalink) pages?
Use the powerful interpolate_fancy plugin which allows for something like
<?$path_info unlike="(^[^\.]+/?$)|(^$)|(index\.\w+$)">writeback stuff goes here</?> . What this says is "if the URL/path_info doesn't look like a directory
(e.g. /some/path/), isn't utterly blank (e.g. /), and isn't an index
page (e.g. /some/path/index.html), it's an individual entry page, so go
ahead and include the writeback bits."