Not yet but thanks for the reminder - I was going to try mint spray on slugs.
from ATTRA article on slugs:

Other options include use of pennyroyal as a slug barrier or perhaps a mulch. Pennyroyal and some other mint oils contain pulegone, a toxic monoterpenoid that acts as a feeding deterrent.
http://attra.ncat.org/calendar/question.php/2006/06/05/what_can_i_use_to_control_slugs

And in Rodale's Organic Gardening mag. Aug-Sept. 2005: A study found that spraying a soap blend - one capful Dr. Bronner's Peppermint Castile soap mixed in a litre of water - on plants and the surrounding soil once a week repelled sluigs and snails, along with earwigs, aphids, spider mites, ants and mealybugs.

Yes.. it is really an amazing thing. In the Garden it seems to keep away evrything, but don't spray your flowers of butterflies and bees will not go near them. I use Mint poision while camping and canoeing .. even keeps away deer flies. I have used it inside my house for my plants and for roaches and ants. Over all it is one great evnironmentally friendly product.

It will also, used weekly, discourage the mice from coming around. 'don't know about rats or voles.

You mentioned your ornamental flowers, but make sure you're not spraying it on fruits and veggies that require insects to pollinate or you won't be getting much yield!