I swear it works, and it's nothing earth shattering - a pair of loooong wide leg trousers, heels (even 2 inches will do) and a top that skims the body (i.e. nothing form fitting or even waist defining). The idea is that you look long and lean, and it's amazing.
I wore this outfit last week and several people who see me on a regular basis asked if I had lost weight, and one person said I looked particularly skinny that day, everyone loves to hear that.
So, for examples of each piece -
The Helmut Lang pants on sale at Gilt today would be ideal - there are two different wide leg trousers, one black wool pair and a lighter pair (both in fabric and color). For invitation to the online sample sale click here. They are an incredible deal - around $100 for very well made and timeless trousers that usually go for much more.
If you don't want to go that route -
These Sanctuary trousers (on sale!) would work well, just make sure they are longer on you than they are on the model (they should go pretty much to the floor) -
These AG cords would be an easy way to recreate the look in a casual way -