There are many differences between commercial 3D printers and hobbyist equivalents, including build quality, size, ability to print in color, etc., but now there's one item that might be crossed off the list: the ability to print in more than one material.
The RepRap team are working on a "head changer" that would enable two or more materials to be used during a single print operation. Imagine printing tweezers with a silicone grip - which was actually accomplished in the image above. The approach is to use a "bowden" extruder and build a carriage for several of them.
In their post, they describe a model that supports up to three such extruders, but the build quality is somewhat degraded. Needless to say, it's very early in development, but when successful, it will bring many more options to low-cost 3D printing operators.