Be careful with ring designs, because of the way that you inevitably need to structure things, you end up needing supports on at least a few places. Unless you design it with a flat face which faces down against the bed, and you use a material which is really good at bridging like PLA can be.
Or you use a printer which isn't FDM. The sintering printers like Shapeways uses are great for things like rings and other designs which require consistent support during the printing process, because there held up by successive layers of powdered plastic which has not been heated into fusion by the laser.
Those are some pricey printers, however, and we are probably not going to have them on our desktops. Though they do exist!
Jewelry design has a huge, huge following in the 3D printing community if you go digging. The flexibility of being able to specify a given shape for a particular use is a big deal for some folks and that segment in particular is pushing a lot of the desktop metal printing development that you see going on.