The one problem is that circuits thus printed are irreparable; once they break (or if a mistake is made), they're junk, which would increase the volume of stuff being thrown away (especially since you can always print a new gizmo). Perhaps someone will come along and invent a nanodisassembler which chews up dead circuits, salvages useful chemical compounds and stuffs them back into printer cartridges (or makes some other use of them)?
Also, I wonder whether the electronics industry will demand that all such devices be fitted with mandatory "digital rights management" technology to prevent people from pirating gadgets (or indeed printing illegal SACD rippers/Macrovision killers/portable OGG players they downloaded from an underground file-sharing network). Or perhaps whether all such printers will watermark their output with the time and GPS coordinates of manufacture, allowing illegal gadgets to be traced to their creator. Which will work, until someone prints a noncompliant circuit printer and uses that to print more copies of itself.
This may be the coolest thing I've ever heard of.
Of course, in keeping with current practices, the printer will retail for $5 and each ink cartridge will cost $700.