Do 3D printers get you all hot and bothered?

They are a PITA for sure.

Yeah. From what I've seen the edges and surfaces are always rough. Maybe they'll improve or I've only seen junk examples.

to be fair what my son produces has always been very well finished - he made bulbasaur planters for friends and they were satin shiny and well finished...  The problem seems to be unreliability and how utterly often the print fails/nozzles get blocked etc.. but then again he's only had his a few weeks so is still learning... 

He's going to make me a cup holder for the car :)

The abilities and quality is all over the board with them.   The quality of the printing substrate varies on supplier.   The types of material they can print varies.
The one a friend has comes out pretty rough but finishing and polishing is to be expected from any manufacture process.
Depends on what you want to make I guess.  The main issue I've seen with people using them is many times injection molding or machining would be more economical and produce a better product.   So unless you come up with something very unique and with high desirability it becomes hard to sell the goods at a decent volume at the needed price to justify the work and machine.  It's a very slow process and doesn't have the ability to churn out consistent products at any kind of clip.
Creating special order and custom things people can't get anywhere else seems to be the most practical model of business with them.   Say car interior replacement parts and custom plastic dashes for example.

I wouldn't suggest anyone getting one unless they can afford it as a hobby to see if it grows into something else.  Gouging the pocket book to try and start a business isn't a goos idea but that's just my unsolicited opinion about it.