It all depends on what software you run under it, certainly Java does not help in this context. A few days ago I had Debian+lxde running on one of those very small chinese mini netbooks; I can't check now what's the CPU, but it's a 300 MHz one with only 128MB RAM, and the system boots from the SD card (the laptop comes with Win CE). I wouldn't call it snappy for sure, but it's useable.