The biggest problem with 3D printing is that you still have a fairly limited range of materials that can be printed: anything with significant amounts of hard metal (steel, aluminum, etc) has to be forged or machined, and don't even get me started on the viability of semiconductors at the moment - at least not with the kind of hardware consumers can afford.
It's also not cheap: the raw materials for printing still cost more than buying the same product from a retailer. The only real advantage is that some materials can (in theory) be melted down and re-used. If you want to have a third party print something for you... be prepared to spend some serious money. At one place nearby that does printing for hire, they have a $100 price tag on an 8" figurine.
Personally, I don't see 3D printing - at least not in its current incarnation - as being anything more than a way to create prototypes, solid visualizations of virtual objects, and one-off specialty items. Items with even simple electronics will still require assembly.
I don't think 3D printing will ever become the "Star Trek Replicator", but I think the technology will become more useful as time goes on, especially for small manufacturing runs of simple items.