Privacy - A Thing from the Past?

A new service, called Blippy, was released. It is similar to Twitter, except that it posts your credit card purchases online, so people can see what you are buying, where from and for how much. You may pick one or more of your credit cards and post their transactions online or you can allow websites, like Amazon, Netflix, or iTunes to make your purchases public.
I was very sceptical when the service was announced several months ago and I was surprised to find out today there are people who are posting their transactions. I do not think I am going to use this service? Would you and why?