My friend was selling his guitar cheap. He'd bought it years ago planning on learning to play and never really gotten around to it. I picked it up for next to nothing as a spare to keep around.
It's not a high quality guitar. It has cheap parts and the construction is shoddy. An SG with a bolt-on neck? That's just wrong.
It's not all bad. The pickups are actually surprisingly aggressive and decent sounding.
By far its biggest problem though was the fret work. After many hours trying to get it intonated, I still couldn't get it set up properly. The neck was straight but the frets were uneven and no amount of saddle sliding was going to fix that. The lowest I could get the action without it fretting out after a lot of work was still what I would call "very high".
So the guitar sounded decent if you stuck to the low frets and didn't mind really having to fight to get the strings down, but wasn't good for much else.
Soon after I got it, my roommate decided that he wanted to switch from playing bass and really learn to play guitar, so I lent him the epiphone and he dutifully learned his chords and scales on it. The high action arguably helped make sure he learned to play cleanly. Eventually though, he got a decent guitar of his own and the Epiphone went back to just taking up space in my room.
Around that time, I discovered the strange but fascinating world of fretless guitars and a seed of an idea was formed in my head.
It's not all that difficult to do a crude defretting of a guitar. Basically, you get a soldering iron and some end clippers and one by one you heat the frets with the soldering iron to melt the glue that holds them in and then work them out with the end clippers. When they're all out, you fill the fret slots in with epoxy, let it dry, then carefully sand it down (with a radiused sanding block) till it's flat. You also need to lower the action significantly which involves sanding the nut down. I actually ran into a wall of how low I could get the action when I got the bridge lowered all the way. To get it any lower, I'd need to find and install some kind of new bridge that can go lower than a stock tune-o-matic.
It was easy and fun. I documented the whole process on flickr. On the recommendation of what seems to be the consensus of the fretless guitar community, I strung it with flatwound 11's and dropped the tuning down a step to D. Apparently, without the frets to protect it, a rosewood fingerboard would quickly get chewed up by roundwound strings.
The result of the transformation is impressive. It has less sustain than it did with frets (ebows and sustainiac systems are popular tools for compensating in the fretless world). The combination of the flatwound strings and the damping effect of the fret point being flesh instead of metal makes it much darker, mellower, and softer sounding than it was. Luckily though, the pickups were incredibly bright and aggressive sounding to start with so the result is actually very nicely balanced (though no longer aggressive enough sounding for serious metal crunching).
With the low action, thick flatwound strings, and low tuning, it's quite pleasant to play now. Well, there's the whole "fretless" thing that takes some getting used to I guess. It's really a different world. It doesn't take long to retrain your hands to basically find their way around for playing single notes. It does force you to get more precise though since you have to fret it exactly at the right spot with no margin for error. Chords are a different matter. Some basics like two finger power chords translate pretty well and you just have to get used to bringing your fingers together as you move up the neck. Other chords, particularly ones that involve two notes at the same fret on adjacent strings, are pretty much impossible. When you play those chords on a fretted guitar, your fingers can be staggered a little and the fret keeps it sounding right. On the fretless, when your fingers don't have room to be perfectly vertically aligned, you just can't get those two notes to work together. The result is that while I wouldn't say the fretless is much harder to play than a regular guitar, it's true that you absolutely can't take the songs and patterns you learned on a regular guitar and immediately translate them to the fretless. You kind of have to go back to the beginning and come up with new material and figure out new patterns. I haven't even really gotten into experimenting with just intonation and microtones yet (I need a better tuner). All in all, I think playing the fretless has really helped me improve my playing. My ear is better, I've had to get more precise and tight with my left hand, and it's forced some additional creativity out of me.
This modification really turned a nearly worthless guitar into something really interesting, fun, and educational. If you have a "disposable" spare guitar laying around and a fretless guitar sounds at all interesting to you, I recommend giving it a shot.
It's still not a great guitar though. After a few months of temperature and humidity variations, the epoxy that I filled the fret slots with now sticks out just slightly. Not enough to fret the strings, but enough that the neck doesn't feel totally smooth under my fingers. So I need to re-sand it to get it smooth again. I can see why more serious fretless player tend to just replace the entire fretboard with a smooth block (and usually something harder than rosewood like ebony or even brass, aluminum, or glass).