While pair programming I will say something like "just click on it with your mmb" and I always hear "what's that do?" I have yet to work with a single developer that uses the mmb. I live and die by mine. This doesn't include the "I don't have a MMB" Mac club.

It is quite handy as a clipboard in Linux distros.

That said, I learned the hard way the switches put for MMB are often subpar and fail quite fast. I replaced an Omron (?) switch in a Logitech mouse... twice. Thankfully the current Corsair M55 (pretty basic wired gamer mouse) goes strong.

My "middle mouse button" on my Mac is the Command key. It does the same thing as the middle mouse button when combined with a left click.

Yes, there is also a ctrl + left-click feature in Windows and Linux, but it isn't nearly as convenient as the middle mouse button.

And on a laptop, 3-finger tap on a touchpad can act as the middle mouse button. May have to enable it, though.

I'm guessing you mean clicking the scroll wheel, which is awesome and I'm surprised that's rare.

What? It's much worse now, I routinely see rich web apps which refuse to open a detail view in a new tab, and reject the attempt by the middle mouse button to do so. Instead I get a huge noticeable lag to switch between the two. Ick.