I would never have one as they are inherently unsafe; children have sustained fractures while jumping solo and just hitting the bed too hard. A local adult, who taught trampoline usage, was killed when he landed a little off and broke his neck.
I know that lots of people have had trampolines for years without any problems; I also know people who skydive without problems, but I still think THAT'S dangerous, and wouldn't do it! (I also don't have a home pool, although my children have both been swimming since toddlerhood.)
And yes, more children are hurt in auto, bike and water related accidents than on trampolines; higher numbers of children also ride/play in/on them and do it more frequently. The injuries per trampoline usage is significantly higher, especially since they are only seasonal in many areas. If all owners could use them year round, the number of injuries could be even higher.
The bottom line is, I need to have my children riding in cars in order to function in my environment. Bike riding is considered a neccessary skill; my daughter is overseas and that is her major form of transportation. Learning to swim might save your life some day. I don't feel that the rewards of a trampoline outweigh the risks. Someone else might feel that they do.
