Hi Dave,
I just mean that the buttons are designed to hold up to millions of clicks, or not. I would guess that they are - since this is Logitech's top of the line mouse (though not specifically called a gaming mouse).
Here is a useful review - that mentions the buttons are rated for 10 Million clicks:
So, not as long as the 60 Million keystrokes on my new Corsair K70 keyboard with Cherry MX Red switches - but pretty good, nonetheless.
I like that it has features that are useful for Macs - I upgraded to the latest version of OS X and it broke my Magic Mouse.
I am using a Logitech M-705, which does not have very robust buttons. It has AMAZING battery life - like 3+ YEARS, but for me, the buttons break before the batteries run low.