The remark about fragmentation is very true Armin, but unfortunately I don't think it's in the "risk" stage anymore, it's a reality today. There is Qtopia for the Sharp Zaurus and Archos PMA lines and some phone-like devices, Maemo for the Nokia ITs, another Linux coming for Palms, etc. And that's only the corporate efforts, but the various communities are perfectly capable of fragmenting themselves too : look at the sheer number of competing (and mutually incompatible) distros for a popular but confidential platform like the Sharp Zaurus, you'll probably need the fingers of both hands :-)