Chrome does that spinner on Windows, too, as does Firefox. I'm glad for it but I like the progress bar idea, personally. It gives me a sense of progress. It is kind of like being on hold. It is the difference between "Please hold" and "You are number 4 in line. Please hold."

Sidenote: The Amazon App Store app on Android does something similar. I've seen other apps do this as well but I can't think of them at the moment. Is this a design pattern we will see more of like the Ajax spinners of the Web 2.0 craze?