I used to LOVE communals as a teenager, out shopping with my friends. Then, the first time I went with an ex-boyfriend, I left my bag (stupid me - should have left it with my ex) with the clothes I was trying on and went out to show him. As I got back I caught the woman next to me darting away from my bag with my purse in her hand.
There was a huge fuss with the store manager and I had to prove the purse was mine (luckily I had a photo in there and a St. Christopher that I was taking in for repair so could prove it easily) as she wouldn't return it and tried to brazen it out. I think because she was an older woman (30's compared to my 18), the staff wanted to believe her.
I've never used one since. It was a bit difficult in the good old days, but thankfully, most of the shops I tend to go to have individual changing rooms these days. If they haven't, I check out the return policy and take stuff home. At least with individuals, you can close the curtains and hide your bag under a pile of clothes if you need to leave anything for a better view.