some of the early 3d printed stuff I saw - was rapid prototyping for a piece of kit the company I was working at was scary - it was great that it worked, but it was very brittle plastic and only really any good for use as a visualisation tool or as a plug for silicon moulding to make a slightly more solid version - but (for example) those Garmin mounts I linked to feel to all intents and purposes like they've been carved out of something like Delrin - certainly strong enough that I don't worry in the slightest about sticking a £400 acessory on 'em and hooning downhill at 50mph or so.
I actually saw some footage of a company that are using 3d printing technology with titanium dust and lasers (excuse the non-techie way of explaining what I saw) to actually manufacture custom 3D sections of cycle frames, tubular to solid sections that can be welded to drawn titanium frames...
http://chargebikes.com/products/freezer-ti-with-3d-dropouts/