If I'm sharing information on a setup script for example, and I share it in a pastebin or a Github Gist, are there any security issues if the posted information includes absolute file paths to real resources on my server?
If your server is otherwise secure then its simply not recommended to do so, but poses no immediate threats.
However, if your hosting a web server there are extra risks involved such as SSI (server side includes) which will allow individuals to access those paths. You may want to double check your server user permissions and vulnerabilities first.
Its rarely necessary to use absolute paths and is just an extra risk. Your just laying our breadcrumbs for someone with malicious intent ;)