Generally, I think they've been somewhat effective, though I know they annoy a lot of drivers. I also notice that for the most dangerous vehicles (large pickups and SUVs with high front heights which make it more likely a pedestrian will be crushed under the wheels rather than falling onto the hood), the speed hump "solution" is fairly ineffective; these vehicles' widths tend to be enough to adequately clear the humps without slowing down much. So, we're effectively slowing the safest vehicles, but still failing to stop the most dangerous ones.

Ideally, we do things like raised crosswalks and planting trees along street edges and doing road diets and then start separating out pedestrian, cycling, and vehicle uses... but I won't hold my breath (I will raise it with the city councilors I know, though).