I think Radwanska and Li were seeded to get this far. Stephens looks one of the more promising youngsters, and her game seems ideally suited to grass. Based on what little I've seen of her I reckon she could win Wimbledon one year if not this one.
The big shock is obviously Serena going out. Hopefully she'll fade now and give some new faces a chance to win some tournaments. Still reckon she'll win the US Open though.