Less trouble with the printer itself than the steep learning curve for the drawing software. I'm using EAA's free version of Solidworks. This is a professional package that does little hand-holding for new users. There are software packages more suited to beginners.
I have a relatively cheap printer (Dremel 3D20) and have had little problems getting it to work. This is a basic starter unit, using the common reels of plastic filament to print. It is a completely integrated unit with a full enclosure...it doesn't have the space-frame hobbyist look that some do. I have it in my home office. Uses a lot of space, but doesn't make the place look like a workshop.
One thing to keep in mind that these filament-type printers can't print any random blob. Anything that comes up at an angle has to have supports when printed; either as part of the design, or the automatic supports generated by the printing software (which have to be stripped away when it is completed).
I've done relatively few "useful" things, the majority of the stuff I've printed have been fun projects. In the "useful" category is an adjustable floor heat register (the vent was slightly undersized, and I used the metal grate of a commercial unit and 3D printed the vanes), stands to display aircraft instruments and challenge coins, a replacement knob for an antique radio, and a custom bracket to hold a test tube (for testing autogas for alcohol).
Fun projects include a replica WWII gunsight, a "Buck Rogers" rocket to work as a stand for a mission patch, and a full scale, non-firing replica of a Lewis Gun.
Most of these projects have a combination of 3D printed and non-printed components, such as the base for the gunsight and the wood structure of the Lewis (the drum is a commercially-available part, the barrel was turned on a lathe).
Most of the things I've done haven't really HAD to be done on a 3D printer, but it does take the stress out of trying to get the thing right the first time to avoid having to keep starting again from scratch. The heat register is a good example... having to attach 3D parts to a commercial grate, and having the vanes adjustable. First version was too tight, go back to Solidworks, adjust a few dimensions for the various parts, and re-print. Much easier than hauling out the right wood, re-cutting the various pieces, sanding them to fit, drilling new holes, etc.
The downside is the AMOUNT OF TIME the printer takes. It isn't a magic replicator. The Buck Rogers spacecraft (done in two parts due to the limits of the filament-type printer) took a total of twelve hours to print. The stand took almost as long. Fortunately, you don't have to sit and watch it, though an occasional check is a good idea in case the filament broke or the unit isn't adhering to the build platform.
Ron Wanttaja