We've seen many applications of 3D printing to a wide variety of situations, but this one is pretty interesting: Indiana-based research scientist Shane Graber has been using his MakerBot to produce a variety of specialized items for his salt-water fish breeding experiments.
He's designed an incredibly simple brine hatchery composed of a base that's 3D printed on the MakerBot, and a cut-off 2 liter bottle. This is significantly less expensive than a store-bought equivalent and you can make as many as you need.
A second experiment involved making a sponge filter. Graber used PLA instead of ABS to ensure the filter would sink to the bottom of his salt water tank. By installing a hose and wrapping inexpensive sponge he's created a do-it-yourself sponge filter.
These are simple objects, to be sure, but the point we want to make is that when one owns a 3D printer there are many such situations where even limited 3D design skills can produce very useful items. You don't need to design intricate objects all the time; simple ones often do the job. They don't even need to look pretty.