There is a fascinating post on the RepRap blog on using inkjet sprayers while outputting on a 3D printer.
It would certainly be nice to be able to lay down waxes, resins, conducting ink and all the rest in a RepRap with the fineness and precision that inkjet could give. We would probably want to use Epson inkjets, which use piezoelectric mechanical pulses to eject the ink drops. All the other systems boil the ink by resistive heating in a tiny chamber to eject it. The piezoelectric systems will obviously be more tolerant of funny polymers and the like, which might not take kindly to being boiled.
Apparently a lot of preliminary work was done by Amberish Jaipuria who published a paper describing his findings.