We currently use it with our clients, and we haven't had any problems with it. From the client side, when you invite someone, they get sent a link with a url i

We currently use it with our clients, and we haven't had any problems with it. From the client side, when you invite someone, they get sent a link with a url in, that automatically logs them into the image, and it's one click image commenting in exactly the same manner as the designers side. They also get emailed when new notes get added by you, with a link in each email so they can go to the proof. If we have any issues with clients, we'll be the first ones looking to update the UI...without the clients, it's pretty much a useless tool after all.