Notes for package maintainers (and perhaps suitable for finding solutions to 
your problem with no hddtemp being displayed):

This version now has optional compile-time support for libsensors3, hddtemp and
ACPI stuff. Thus, when creating packages, you have the choice to deliver a 
package with all features, which then strongly depends on all of the compiled-in 
features and libraries.

hddtemp is no longer searched at run-time, it is only enabled at compile-time.

If you know of any further OS-specific interface or system library that might be worth including, please tell me. 

For hddtemp to work for users in the plugin, it must be setuid root or a hddtemp daemon must be running. If none of this is the case, the plugin can't display the hard disk temperatures. A possible workaround consists of adding a wrapper script as option to --with-pathhddtemp, that will call sudo on hddtemp.

Theming: You can put a customized style file globally under 
         /usr/local/share/xfce4/panel/plugins/xfce4-sensors-plugin.css 
         or locally under $HOME/.config/xfce4/panel/xfce4-sensors-plugin.css.

