What do you know about other important materials for future applications in spintronics? What materials currently are the most promising for spintronics?
Yuriy, I'm not an expert on this one, but it might have to do with the "conductivity mismatch" experienced by the many who have tried to do high polarization spin injection at (magnetic) metal - semiconductor - interfaces. So, if ZnO could be used to better match magnetic materials to semiconductors (either by making it a semi-magnet or an interface to e.g. a magnetic oxide (Fe3O4)) then this would be a very letigimate reason.
Typically, when one speaks of magnetically doped semiconductors, the aim is to have a strong coupling between the magnetic ordering of the "dopants" and the free carriers so that the ordering is in fact mediated by the carriers (typically holes). These magnetically doped semiconductors could then be used for efficient injection of spin-polarized carriers into "regular" heterostructures, or as spin-selective source/drain regions of transistors. Spintronics is however much broader han just the application of magnetically doped semiconductors, as can be seen from e.g. the link list given in one of the answers above.
TM doped Zno is generally thougt to be promising because doping could be "easy" as Zn is a TM, too. Also there are many reports that claim to observe magnetic coupling between carriers and dopants. There are two main challenges: many of the TM elements tend to form non-stoichiometric compounds with O, and p-type doping of ZnO.