I was reading my favorite garden forum the other night and ran across a thread on coffee grounds. While they proved unsuccessful for germinating seeds several people used them as soil in potted plants.
They also reported success propagating things like roses and other shrub like plants. Branches were cut, lower leaves removed, rooting hormone applied and then potted in used coffee grounds. All people doing experiments reported seedlings did better in coffee than in soil.
Used coffee grounds act as a mild fertilizer ~( 4, 1, 3 ).
The caffeine in coffee is thought to be a neurotoxin to several unpleasant little critters in your soil such as slugs. I found reports stating they both helped and harmed nematodes. Nothing conclusive either way there.
Grounds are acidic so are a great mulch for your acid loving pants.