On my recent flight to JFK I had a crew member on my side of the F cabin who wasn't First trained. It seems they had a surfeit of crew on board and they were asked to help out up front. They did a good job but you could tell the difference in service from the person dealing with my partner's side of the cabin. Nothing to complain about, just little touches that showed different levels of familiarity with the whole product.

I think it's good to give crew chance to help out in different cabins - the wider the experience they get, the better they can do their job?