The forces of the DAO pattern are that they allow you to create a nice abstraction layer of the actual storage system. They provide a more object-oriented view of the persistence layer and a clean separation between the domain and the code that will actually perform the data access (straight JDBC, persistence frameworks, ORM or even JPA).
If I had to cite a weakness, well, I'd say it's another layer... But I guess this is the price to pay to not tie your code to the underlying persistence API.
