Good addition to a compost pile and reputed to deter slugs. The acidity of UCG's is a bit overstated - generally, most of the acidity is leached out with the coffee itself, leaving the grounds very nearly neutral in pH.

The Soils forum has compiled this helpful bit of info regarding coffee grounds:

Here is a link that might be useful: Soils FAQ - coffee grounds

I saved our coffee grounds and put them around my ligularia and a hosta that the slugs just loved. It seemed to help and there was less slug damage. It also fertilized the plant and it smells nice.