My brother uses one of these service bureaus for his 3d modeling work. He creates cast pewter objects and uses the plastic as prototypes. Their service is not as inexpensive as you think and the quality varies quite variably both from company to company to the ones that run the equipment. The quality has nothing to do with the equipment, but a lot to do with the quality of the operator. There's a lot more than just printing the object out, and these people do not want to take the time to ensure the object is oriented properly for output. If it's oriented the wrong way, the build lines can affect the details and even the smoothness once the part is printed out. The finished product is not as finished as you think either. The output still has to be cleaned up at times, again this depends upon the quality of the printer, operator, and the type of part.
The cost of these printers of course has come down and still the quality varies. The top-of-the-line models cost $30,000 and up while the hobby end ranges from $500 for a kit printer to about $1500 which is a decent hobby-quality printer. I saw a $1500 printer at the Big-E show this past winter. The output was quite nice, but not good enough for my brother's work since he needs a much finer dot-size needed for casting.
Keep in mind that this is still a fairly new field, and like desktop publishing, the quality and cost of these machines is going to change rapidly as the market plays out. Right now with so many numb nuts getting into the output, there will soon be a lot of equipment for sale cheap as they go out of business. While this sounds great, what you don't want to do is purchase some much older, out-of-date, used equipment. Remember these use a deposit system of melted plastic (like melted crayons) that in some higher-end systems is burnished down, and is placed in layers. This can be an issue if the printer was left sitting since the plastic will clog the heads and the lines as the printer has to remain on so the preheater will keep the plastic from clogging everything. I say this from experience while I was at Polaroid. Their DryJet printer used this technology to print printer's ink mixed with a wax on to paper.
John