Well I'm not exactly trying to build robots with it or anything.
The print resolution is actually fairly good (0.1mm on most printers), as long as you have tons of patience. Usually people struggle because they try to get instant gratification, and these things just aren't capable of those speeds. That said, if you're not terribly concerned about fine detail, 0.3mm is much faster and can run at higher speeds too.
There are two plastics that are most commonly used for these printers. PLA and ABS. You've probably heard of the latter, it's used in damn near everything consumer-oriented, and holds up fairly well under stresses and heat. It is harder to use, but it's not impossible. Some printers do a better job.
PLA on the other hand, is super easy to use. It doesn't even require a heated bed (although it's even easier to use if you do), and is somewhat biodegradeable (won't do it in your backyard, but it doesn't take much). It's primary downside compared to ABS though is the low melting point. It'll get soft in a (very) hot car in summer, and lose its shape somewhat.
You're not going to make money off of it or anything, but it's really fun to use for hobby stuff. The cheaper printers, like mine, require a lot of fine tuning, and I wouldn't use it for mass production, but it's great for one-off stuff. I've printed stuff like cups designed to hold screws temporarily, fan grills, replacement knobs for some of my older audio gear, a couple toys for my nephew, etc. I especially like printing custom enclosures for my microcontroller projects, since that's the sort of thing you can't really buy off the shelf. It's form fitting to whatever purpose I need, with the mounting holes and all.
In the end, if you're planning on buying a 3D printer for these reasons:
1. Mass production
2. Off-the-shelf models/etc
3. Large items
Don't bother. You won't save money and it's just not really ready for that yet (but at the rate they're improving, 5-10 years that could change dramatically).
If you're buying a 3D printer for these reasons:
1. Custom models (architecture, figurines, etc)
2. Customizing normally off-the-shelf parts (fan grilles, etc)
3. Printing hard/impossible to find pieces
and don't mind the upfront time and money investment, it's definitely fun. It's really freeing and exciting to have the realization sometimes "man, I wish I had something to hold this up, or fix this", and then realize for like $0.10 worth of plastic, you can.