Brian_Mathato, since he wants to have the summary in the subject,he cannot expect something. It will be different each time.
Marcoaldama, you can create an incident even if there is nothing that says "incident" in the subject but I'm afraid that you won't be able to use the subject as the incident summary.
If you want to try it, you have to take a look at the filters you have in place. There is probably one that looks for "incident" in the subject. You can create a new filter and add it at the last position. For the filter, I think (.*) will do the trick. Simply set action as Create and Object as incident.
And remember, if you start to have too much mailbox rules that may overide themselves, you can have several mailbox and define diffrent rules for each one of them.