We have Email2Case configured to add inbound e-mails to their respective case when they arrive.

I'd like to write a trigger which fires when such an e-mail arrives (so that I can potentially move the case to a different state).  I can see two ways of almost achieving this, but I can't find all the pieces of the puzzle.

1. I could create a trigger for when a new task is created, except I can't seem to find a way of getting at the e-mail assocated with the task -- is there a way to do this?

2. I could use the InBoundEmail handler to handle the e-mail, but then I need to manually go about working out which case it relates to, which seems a little heavy handed -- is there a way to have SF give me the Case# for an e-mail if it spots the reference tag?

Is there a simple solution I'm overlooking here?

Cheers