The way that 3D printing technology is ramping up so quickly, instead of asking "What can you print?" we should be asking "What can't you print?". There's no better example than the jet engine turbine shown at the World Maker Faire last week by Kraftwurx.
Kraftwurx is essentially an online fulfilment company that enables designers to upload their creations, setup a storefront, and take orders, while Kraftwurx does all the 'behind the scenes' grunt work by processing the orders, printing and shipping the items, processing the credit card payments, and delivering a check to the designer. It's not a new or unique business model, and has been successfully applied to other markets, like photography and t-shirts, in the past. Kraftwurx's spin is to apply the business model to 3D printing coupled with a lot of applications and design know-how.
The jet engine turbine they had on display at Maker Faire was a good example. It's still in the prototype phase, and is intended for use in a model aircraft rather than anything life sized. Still, it was quite impressive to see first hand.