[1] https://help.ubuntu.com/lts/installation-guide/ppc64el/ch02s...
The things that didn't were typically lesser used desktoppy things or more community written software that didn't take endianness into consideration. If you're not afraid to dig into sources alot of things only took adding an endianness hack / byteswap to certain lines to make things work properly.
Also to check into are some languages/compilers/interpreters simply might not have a backend for your CPU. If you use any of these critically you might double check; common things like perl/python/java/ruby should be fine.
I'd expect most server-side / computation oriented things should be fine- desktop, etc, not so sure especially since noone is making any power based workstations these days, though remote GUI mgmt is still useful in some annoying cases
Overall stability, barring per-platform issues should be fine as well.
basically, if you don't mind getting your hands a bit dirty from time to time, it should be okay; not sure of support for this particular board / firmware/ etc though..
hopefully someone with recent experience can confirm
That being said, there's probably a lot of libraries with x86-64 ASM kernels in them which will run slower if they have to use the generic C/whatever version on power.
If you are a dev who isn't being paid by e.g. IBM or Red Hat to work on ppc64le stuff, it seems hard to get access to running your code on real hardware and running on qemu doesn't really make sense for optimizations.
It seems to me that the ISA could benefit from scaling down so that more developers had access.
If they can keep this up, I could actually fork over the money for the 3rd gen.
Oh wait, wrong company.
I personally run OpenBSD on all my (Apple) PowerPC hardware; it seems to work a lot more reliably than the Linux distros I've tried (in particular, I remember the install process for Debian being rather painful on PowerPC due to OpenFirmware, while OpenBSD is just as easy as it is on x86: mash the Enter key until you have a working system; at most, I sometimes need to tweak some boot settings at the OF prompt, namely if it was previously running OS X).
Debian PowerPC version has a few bugs but at least the desktop package selection has been decent, shame that the port lost the official status.
The XServe and Power Mac are in storage right now, but I'd like to get the Powerbook upgraded to 6.1 eventually (I want to stick full-disk encryption on it, too, so I'll probably just blow away the existing install and start from scratch).