It's actually pretty easy to do. I've seen several Windows, several BSDs and linuxes as well as some open-solaris derivative on x86 Macs.

The PowerPC macs are a bit less well supported just because there are fewer distros for PowerPC, but on the other hand, since apple's pretty much abandoned them, going with linux or a BSD has its own advantages

_I was not aware it's "easy" to run other OS's on Apple hardware. Knowing Apple, I'm still not sure I believe it._

I run linux (arch now, but once ubuntu) on a MacBook5,4. It's somewhat harder to get set up if you want to dual boot (the dual partitioning scheme is finicky, and although linux doesn't need it, OS X forces you to use it if there's a foreign OS, ugh..). See http://wiki.freebsd.org/AppleMacbook and https://help.ubuntu.com/community/MacBook .

Only one proprietary driver (for wireless) is needed - the rest Just Works. (And flash plays smoother than on OS X :P )

I tossed a ubuntu cd in my MacBook Pro, rebooted holding down option, and it booted up just fine. Could it be easier?

One thing that could be easier is booting MacBook Pro from USB stick. A Unetbootin that works on Mac, and builds usb sticks bootable on Macs, would be good.

Or maybe bootcamp could mention Linux.

My preference is to use only the bootloader for the OS I'm booting, as opposed to a "boot manager" that presents a menu of OS's. I avoid using chaining techniques the way something like GRUB does. And I don't use MBR's if I don't have to. Disklabels alone will suffice. So the stick contains only an OS-specific bootloader and the OS, usually just a kernel with embedded ramdisk or a loadable kernel module containing a filesystem and userland. I keep it very simple.

This works well for me with PC's. Would this work with today's x86 Macs?

I installed Windows as dual boot on a friends Mac. It's far easier than installing it on a windows PC. Put in the windows disk and follow the Apple instructions - it includes all the drivers and even gave advice about sharing files .