I'd love a low-power, high-performance ARM notebook. I'd be happy with MIPS or Loongson (Chinese MIPS clone) as well. Debian already has a full-blown ARM port and I'll bet they could get it working on an ARM netbook in a day. Ubuntu would undoubtedly be soon-to-follow.
There was an ARM employee at DebConf with a protoype ARM-based netbook. I forget whether it was running Debian or Ubuntu, but in any case the software is basically ready.
As a side benefit, having multiple widely-used architectures for desktop systems (x86 and ARM) would be a support nightmare for hardware companies that still keep their drivers proprietary and undocumented. Yeah, I'm looking at you, Broadcom and NVidia.
I'm pretty sure Broadcom is already providing drivers for ARM as many home routers run on ARM. As for Nvidia, do they have any chips that fit in the price and power brackets of netbooks?
I see a significant barrier to ARM adoption in GCC's code generator, which is poor and apparently getting worse as the optimisations are more tuned for x86 than RISC processors. ARM, like Intel, has its own commercial compiler but it would probably make business sense for them to contribute to GCC as well, just as Intel does.