[Mikuro]

When do you get the spins?

I think it's more likely that there's something wrong with whatever programs you're using. Some programs are just slow and buggy. Safari is one of them, especially when dealing with animated gifs or plugins.

Even the slowest processors are not so slow that you should get a lot of pinwheels.

Take a look in Activity Monitor to see how much of your memory is being used. It could be that there's a runaway process eating more memory than it should.