if you read the link that I posted along with the opening post; that will answer a lot of your questions about how the Petcube works. It looks to me like not just anyone can access your dogs Petcube, because the article specifically says that you have to authorize the users. However, if there are several members in your family, or even friends that your dog likes, then you could have them authorized to be able to interact with the "home-alone" dog.
After having two trips to the hospital recently for my heart problems; I can tell you that both Chipper and I would have been happy to have had such a device. He missed me terribly when I was gone, and my husband said that he finally just went and hid in a corner and moped when I didn't return after a couple of days.
One time, Bobby did put him on the telephone with me, so I could at least talk to the little guy; but i am sure that he would have enjoyed the Petcube a lot more.
I also think that it would be great for the animal rescue places to use one of these. People who lost their pets would be able to look for them easier, and someone wanting to adopt a pet could also interact with the dog, and see if they would dork out before adopting the dog.