I can't tell you anything about the APUS since I don't have any PPC for my Amiga and therefore not been able to try it out.
However, I have been running linux-m68k for years now and it works like a charm. At the beginning I tried the RedHat 5.1 which is the last stable RedHat for m68k. That worked very well indeed but became kind of old so I moved on and tried Debian GNU Linux instead.
I have been using Debian GNU Linux on my A4k with 040/40 for a few years now and I must say that it works very well. It isn't fast, especially running X, but it is quite fun to fool around with anyway. I have been compiling kernels to try different things and so far I haven't had any major problems. X might be a little difficult to get running from start but once you get the hang of configuring it it won't be a problem.
From start it didn't have any drivers for my CV64/3D so I had to start linux up from the screenmode I wanted to run it in, but now the kernel contains a driver for that so I can use lilo and fire linux up which is a hell of a lot easier.
So, as a summary. Running linux on an m68k is fun and not to difficult, you might have to tweak a little but that's the fun part. I really don't recommend running X unless you have at least a 060. It works with a 040 but it is quite slow and patience is a virtue.
Running the APUS should be a charm if you have a PPC. There is a few more choises for a more updated linux if you use that. I would still recommend Debian since I have fallen for that distro.
