For me personally only really the x86_64 architecture matters, I do have an ix86 machine sitting under my desktop but it is humming along nicely. Everyone really supports these just fine, but here is a thing I don’t get. Why do so relatively few distros support ARM and MIPS. Firstly let’s examine why these archs are important, ARM is widely predicted to take a huge bite out of the netbook market, a segment it is extremely well suited for. MIPS naturally is important because it is the foundation for the Chinese YeeLoong chips which we are likely to see the Chinese market gravitate towards. Being a market of a billion potential users with additonal opening to the west via netbooks this is definitely a place Linux distros should be putting some effort, we have literally no competition here, the first distro to integrate really good support will likely be able to pick up millions of new users over a short span of years. This is also a good target because this specific segment has shown signs of being the first truly open platform we might get, from the BIOS and up.
Having a significant chunk of the netbook market is likely going to be important. It is a good market for Linux as the use cases for a properly promoted netbook do not call for “regular” desktop tasks but more likely a specially designed interface such as is see with the EeePC or the Aspire One.
Thus in my search for a new distro to replace Fedora, one requirement I will set up will be support or planned support for ARM and MIPS. Not because I personally need them right now but because it is my belief that an important piece of the future for Linux lies in this direction.