I'd probably count for four, but if it counts as a new installation each time you format, than more than double that. (No more now though, I've got a Mac. 3) I'd assume it's the same for many users here.
I wish I could take credit for this... It showed up in my mailbox about ten years ago.
What Happens When Engineers think too much about Christmas...
There must be more to life than having everything. -- Maurice Sendak