I know SQ had an issue with this after the Taipei runway accident a couple of years ago. The female cabin crew suffered badly with cuts and lacerations on their feet and there was talk in the Singapore Newspaper of replacing their shoes with something sturdier than the glorified flip-flops they were wearing at that time. Since then havent actually noticed what they wear nowdays...

Interesting to hear this has come up on the radar of other airlines as well...