I (hackmiester) own(s) a MacBook from Apple. Actually, that link is inaccurate - I own a first generation MacBook, while Apple now sells a second generation. In any case, I ran into a few pitfalls as I installed Arch on my MacBook and I'm going to share here how I got Arch running smoothly. Even if you DO have a second gen MacBook, trying these instructions probably won't hurt anything. (If it does, it's not my fault, though!) You might even find these helpful if you have any other kind of Intel Mac.
Setting the scene
Before I started this process, I'd partitioned my MacBook in two using Boot Camp for Mac OS X. This gave me a 10G Windows partition and the rest as a Mac OS X partition.
Step 1 - Partition the disk
Later, when I decided to install Arch, I resized the Windows partition to make room. I used BootIt NG from Terabyte Unlimited. If closed source software makes you uneasy, use parted. Whatever works.
If you use BootIt NG, this process is drop dead easy. If you use parted, you're on your own. :-P
Step 2 - Wonder if your keyboard is broken
After you boot the Arch installation CD-ROM, you will probably find that every letter you type has a long delay, and then comes out double!!! After much Googling, I found this excellent page on the Debian wiki about the MacBook. As that page says, what you want to do is provide the kernel with the "noapic irqpoll acpi=force" options. At the boot prompt, you'd do this:
boot: arch noapic irqpoll acpi=force
Yay, now you can actually run the installer. That's certainly an improvement.
Step 3 - The usual installation... or is it?
Okay, so just when you think everything's going your way, your ethernet adapter isn't detected. Neither my wireless or wired were detected. There was an eth0 interface, however. Dmesg revealed that to be an IP over 1394 device that takes advantage of Apple's FireWire in the MacBook.
I found it odd that the FireWire works but the Ethernet doesn't.
You might be thinking, "But hackmiester! A network connection isn't required for the installation!" However, it IS required if you are like me and have the crappiest Internet link ever, and just want to get a base system going using the FTP install disc.
Anyway, I wasn't sure how to fix the problem, so I decided to do it the hard way. Here's what I did:
(I'm going to look up how to do this now. Basically what I'm gonna do is bridge a connection from my other laptop with FireWire over to the MacBook so it can get an IP and Internet access through the other notebook. Stay tuned.)