So admittedly I bought this pedal only because I'm an incubus fanboy, but I've had it for about two years now and still never get tired of it. I use it with the distortion circuit turned all the way down so I just get the ring mod signal. Yes it's very easy to nail the sounds from 'Glass' and 'Pendulous Threads,' but why not create your own riffs with it?
I personally love the sound of this pedal. The way I have it set the ring mod totally takes over the sound and turns the guitar into a robot...basically. It's not a very clean or smooth sounding ring mod, at least compared to the other ones out there. The Zvex ringtone has a really crisp and smooth quality to it, as do the Moogerfooger and the Electro-Harmonix Frequency Analyzer, but the Gonkulator has this harsh, tinny tone that you can't really get away from.
The drawbacks are few I should say. When you turn the pedal on there is a loud, Bb pop (like picking at the 11th fret on the B string). I know this isn't just my pedal because if you listen closely to the bridge of 'Megalomaniac' you can hear the weird popping in the background =)
Also, while the pedal is on, you can hear the oscillator constantly droning out a Bb in the background. It's not noticeable while playing, but the second you stop it's there. I just turn the effect off when I'm done with it anyway, but it's worth mentioning.
Now the only major drawback on this pedal is that you can't tune the oscillator to anything other than Bb. Pretty much every other ring mod on the market has this feature (the Moogerfooger even has the option of controlling the carrier frequency with an expression pedal), but DOD apparently overlooked it.
I don't want to go through my entire rig, but to give you a general idea my main guitar is a Fender Mexican Telecaster. I also have a Mexican Stratocaster with DiMarzio Area '58 pickups and a 1990 Rickenbacker 330. My sound goes through a total of 23 effects at the moment with the Gonkulator sitting comfortably sitting 6th from last on my board (I keep it after my overdrives and time-based effects, but before my reverb, delay, and loop station). All of this comes out of either a Vox AC30 combo or for live use an Orange AD30 with an Orange 2x12.
I think mine was new-old-stock from a vintage pedal store (it was gift) so it's in better condition than some older DOD pedals. However I do consider it reliable with proper care. I like to think that I treat all of my effects with tender love and care. I have a total of three DOD pedals (Gonkulator, Envelope Filter, and Stereo Phaser) and none of them have ever given me any problems. My bass player, on the other hand, got a DOD Grunge from a friend and it only lasted him a couple of months. But this particular pedal was in pretty bad shape to begin with. The plastic battery cover was missing and the jacks were in a state of disrepair. It just recently died on him at a gig, but the only real problem is something with the power supply jack. It was never really all the way there to begin with, but it finally gave up that night. He's bidding on a new one on eBay though.
I consider all effects to be reliable as long as you take good care of them. But the DOD stuff doesn't seem likely to survive a fall down a flight of stairs or two.
I play in a sort of experimental band (we're big fans of The Mars Volta) and I would say that this pedal is well-suited to my style. I like anything that makes my guitar not sound like a guitar. But if you're looking for a ring mod to experiment with I would recommend either the Moog or the Electro-Harmonix. They're pretty reasonably priced and are still in production. Instead of going through the trouble of finding a Gonkulator and not paying the Incubus fanboy price you can get a unit with more features and cleaner sound for just under $300.
It's the only ring modulator I own so far (I plan on purchasing both a Moogerfooger and a Zvex Ringtone) but I definitely intend to keep it no matter what. It is a critical part of my live rig and I just love playing with it. Sure it's a one-trick-pony, but it's only one pedal, what do you expect? If it were stolen or lost I would be pretty mad about it and promptly replace it when I could. But I mount my pedals to my board with metal plates rather than velcro in order to prevent backstage thievery.