Any way to be sure, that Macs don't come with built-in hardware keyloggers? What the title says. If this is the case, even if you choose to delete everything OS X related and put entirely Linux in your box; you'd still be screwed. Hardware keyloggers sit between the keyboard and the motherboard, and record everything typed to memory (perhaps to be siphoned off to a remote server without your knowledge the first time the machine gets online) Also, macs are famously sealed-off black boxes that how it works under the hood is kept an intentional mystery by Apple.

Well, your thoughts, fellow mac-folk?
Any system can contain embedded an hardware keylogger or trapdoor. Most of them do contain the last one. But a keylogger isn't as easy a task to integrate in a completly undetectable way. A keylogger will have to log.
Here is the weak point where you will be able to detect it.
Whichever is the way to log a keylogger will use, you will see something grow inside (hidden disk space, hidden memory space) or escape one way or another (network, light, radio-wave, sound, infrared).

When I look back at the way some bug in serious software aren't fixed, I can be nearly certain that a keylogger won't stay undetected for long.

A keylogger will talk and bug.

Taking into account the risk involved for any company trying to make such an evil minded choice, and a dangerous one (the keylogger once discovered will also be used by the enemies)
I doubt any risk aware company will take this risk.

From my point of view, this is clearly a vital and an unacceptable risk.