The safety of pressure treated lumber for raised bed gardens has been examined by several researchers.

From what I've seen, the consensus is that the chemicals do leach out of the wood into the soil and are uptaken by the plants in very small amounts. However, I haven't seen any research that suggests the level of the chemicals is significant enough to be of concern for human health.

Of course, the primary concern with using pressure treated wood in raised-bed gardens has been with the arsenic in CCA- (chromated copper arsenate) treated wood. This publication from Pennsylvania State University does a good job describing the risks of using both CCA-treated wood as well as ACQ- (alkaline copper quaternary) treated wood: Environmental Soil Issues: Garden Use of Treated Lumber. With regards to CCA, they state, "Although the plant and human health risks from garden uses of CCA-treated lumber appear to be extremely small, there are steps gardeners can take to further reduce any such risks."

One of the steps they recommend is to use wood treated with ACQ - "This is an alternative wood-treatment chemical that contains no arsenic, chromium, or any other chemical considered toxic by the EPA."

If you are shopping for treated lumber nowadays, I don't think you'll find CCA-treated material in the home centers anyway since its use was restricted by the EPA in 2004. It will be more likely be ACQ or some other chemical.