At least in most cases. From page 67 of the World Trade Report 2009, released today:
What are the effects of dumping on the economic welfare of the importing country? Economic theory suggests that, with the possible exception of predatory dumping, all other instances of dumping either increase, or at worst, have an ambiguous effect on, the economic welfare of the importing country. Of course, for the most part, economic literature has treated dumping as an example of the exercise of market power. But within this context of imperfectly competitive markets, dumping may increase efficiency in resource allocation. In most circumstances, the welfare of the importing country increases as a result of dumping, as consumers and users of the product benefit from lower import prices, even though the reason for the reduction in price (the dumping) may vary.
ADDED: But anti-dumping laws have value nonetheless. From page 68:
Anti-dumping policy can act like a safety valve to let off protectionist steam which might otherwise threaten a government’s programme of trade reform.
