Using HDR instead of Fill Flash — Contrast Looking Natural
Here’s a link to a post that explains how High-Dynamic Range situations can be photographed with HDR technique, without the picture looking like the typical HDR-ed fake postcard effect. And avoiding unwanted reflections from fill-in flash at the same time. To me these tips showed HDR as it was meant to be used: as a technique to get natural-looking pictures in difficult situations.
Just a quick addition: when shooting portraits, probably you want some reflection of the flash (highlights in the eyes and in hair!), so don’t forget about fill-in flash in those circumstances.