well there's always gonna be those few people who "break the rules" so to speak and have great success with anemone's in a nano tank. But generally, its not recommended because they grow quite fast and can take over a tank quickly. That and they're difficult to keep, and if you dont stay on top of your water quality, it can change in a flash in nano.
As for PC's, generally you dont even want to try them with PC's, but then again, there's always those people that do it anyways, and some of them have luck.