I think they make for great bonsai. Granted, I'm very new to this hobby - started last summer. As of a month ago, I have several cuttings in a bucket of water, some as thin as a straw and some as thick as your wrist. They're growing roots, and I'm hoping to pot them later this summer. I love the look of weeping willow bonsai, and given the tree's ability to grow like a weed, it makes a great tree on which to learn. Over the past two months, I've been collecting as many trees as possible on which to learn, not worrying whether they die, and weeping willow is one of them. As Forsoothe says, "go for it."