Stem cells are basically like biological alchemy. You can turn them in to almost anything, including it seems sperm or eggs. Researchers working jointly in the UK and Israel have figured out how to create precursor cells for gametes, you know the bits that combine during fertilization to create a tiny human. There's still a long way to go before viable eggs or sperm can be created in a petri dish, but this is a major first step. The hope here is that one day couples where either partner (or both) suffer from infertility could have a child. The process would obviously still be involved and difficult for the couple, much like in vitro.