Variable Substitution
With the release of Indigo 5 and server plugins, it's now possible for plugin writers to enable configuration text fields to accept special markup that will substitute a variable value at runtime. Any string with the following markup will have a variable value substituted:
%%v:VARID%%
VARID is the unique variable ID as found in the UI in various places.
So, for instance, if one of your actions is to use the Growl plugin to do a notification, in the title and/or description fields you could enter something like this:
Turn on the A/C unit - the outside temperature is %%v:VARID%%.
The value specified would be substituted just before the notification was sent.
Note - not all text fields will support variable substitution. The plugin developer must enable it specifically. Check the plugin documentation to see if the field you're interested in supports variable substitution.