what to do with mushy cantaloupe?

These are all delicious ideas for a good tasting ripe melon, but if it is mushy, and the taste is "tough to eat " and it is really overripe ; you might be better off starting over with a fresh Melon. At the very least just try a simple smoothy ,and if it still doesn't taste right , you haven't spent an afternoon trying to make a silk purse from a sow's ear.

Cantaloupe soup with mint sounds refreshing.

Put it in a blender and add sugar & ice It makes a great smoothie You can also add a drizzle of rose water #yum

In the current heatwave in my area, agua fresca would be my recommendation.
http://www.chow.com/recipes/29745-cantaloupe-agua-fresca

If you have an ice cream maker - you could easily make cantaloupe sorbet out of them. Just make sure to pass it all through a strainer of some sort.

Jam. Canteloupe Jam is a specialty in the South of France, actually they use their fanastic charenteis variety. Check out the Blue Chair Jam Cookbook for a perfect recipe.

my dog loves it!

Just another thought; I've used cantaloupe as a filling for tortellini (with mascarpone and pecorino), tossed it in walnut brown butter, and garnished with prosciutto. Really good, but maybe a little more work than you're planning on doing...?

Some savory ideas:

Gazpacho or chilled soup would be good, too. Maybe with some lime and coconut water/milk.

Or some kind of chutney or savory jam. Cardamom, star anise, mustard seed, etc....or mostarda!

OR, puree and turn it into a vinaigrette to serve with fish. Basil or tarragon would be good.

A cantaloupe granita would be fun too. I recently made one with an over ripe honeydew melon. It was so easy and refreshing on a hot evening. It's just melon, sugar and lime juice blended up. Pour into a flat pan and put it in the freezer until semi solid. Scrape with a fork and devour. :0)

It sounds like it would be perfect to put in a morning smoothie along with some yogurt and a little lime juice. Alternatively, purée it with some honey, fruit juice or sparkling mineral water, and freeze it into popsicles to cool you on a hot afternoon.