Can any distro run on a Macintosh Laptop? Or just specific ones?

Debian
http://www.debian.org/

MKLinux
http://www.mklinux.org/

RT-Linux
http://www.rtlinux.org

SuSE/Novell
http://www.suse.com/

Yellow Dog
http://www.yellowdoglinux.com/

HA Linux
http://www.motorola.com/linux

ELinOS
http://www.elinos.com/

Source Mage GNU/Linux
http://www.sourcemage.org

Mandriva
http://wwwnew.mandriva.com/

Shark Linux
http://www.sharklinux.com

Intrinsyc Linux
http://linux.intrinsyc.com

PLD Linux
http://www.pld-linux.org/

Ubuntu
http://www.ubuntulinux.org/

Gentoo
http://www.gentoo.org

Fedora core
http://fedora.redhat.com/

Kubuntu
http://www.kubuntu.org/

Gnoppix
http://www.gnoppix.org/

Knoppix MIB
http://www.bouissou.net/knoppix-mib/...oppix-Mib.html

LFS Live CD
http://www.linuxfromscratch.org/livecd/

Rock Linux
http://www.rocklinux.org/wiki/Main_Page

For your older macs you need a distribution that supports the ppc(Powerpc) architecture.

Distrowatch is your friend and will allow you to search on this specific criteria

I cannot speak for phantom_cyph, but I know that
what I am interested in is not a long list of
links to distributions that we all know about,
but rather specific recommendations from someone
who actually has experience using one or more of
these distributions, and information about their
system requirements. For example, if I have an
older Mac, say a G3 with 256MB of RAM, are there
distributions that will not work? Is there a
particular distribution that is unusually good
for this hardware platform? Etc.

I have an Ibook G4 running with a powerpc, along with 1,5 GB Ram.
I run it with Debian Lenny, for powerpc and it runs very smoothly, as fast as OS X, but no faster, which I thought it would, at first.
The big difference, IMHO, is that HFS+ gets fragmented quite soon, whereas ReiserFS doesn't. In my experience, at least. So eventually, a ppc mac with debian runs faster than with OS X, with less hassle (defrag, buy a program which does it, boot from an external Firewire HD)
The only glitch is making the wireless work. It's still a challenge. Mine doesn't, but I didn't look into it seriously enough.
Overall, debian on apple hardware is better and better supported. I also found a way to have the "twofingers scroll" on the touchpad, which is a nice feature.
As the keyboard is not "backlighted" (I don't know the word in English), like on Macbooks Pros, I can't tell whether this feature is implemented or not.
Hope that helps
cheers