I think that if you have nice shoulders and good posture, showing off the shoulders are the way to go - if you haven't good posture though, I wouldn't attempt it as it draws attention to the fact.
A nice backless number is good so long as you have your bases covered - nothing too far down and making sure it doesn't come around too far so you 'bare all', so to speak.
I think the best thing to do is to expose no more than one or two areas at a time; I breasts, legs, back and shoulders combo is guarenteed to look a little cheap.
As a photographer, I hope the backless trend sticks. It's so nice to see women posing over the shoulder with such a flattering twist at the waist. It's feminine, sexy and seductive all in one.
1. you better have a clear back
2. you better have short hair, or pull it up
3. theres a thin line between flattering and a fattning shirt.
4. if your boobs are too large, over a C, then you just have that "big" appearance in the front.