I haven't; however I do shorter night rides in the country (mountain valleys mainly) sometimes (2 hours max).

The problems I noted :

1. I need to be cautious all the time, even with a strong light, when going at or above 30 km/h (18 mph), I discover obstacles very late: we cannot see in the distance or on the side, all the things that we usually register without truly paying attention, effortlessly;
2. despite this and the fact that I ride roads I know by heart, I regularly hit holes and all sorts of other road defects that I would almost never hit in day time; small (but dangerous) things like a spray (?) of gravels over the asphalt basically never can be spotted;
3. talking about obstacles, some of them literally jump at you: I meet a lot more animals at night that at day time; a few of them freeze in the light right in front of you (fox cubs, I am thinking of you);
4. I found maintaining the constant attention very tiring for the eyes and the brain: despite the lack of sun, I get that feeling of sore eyes / face skin quickly (it seems to get less true with experience repetition, though, but perhaps it is just because my level of attention decreased too);
5. it also tends to give me a stiff neck because said attention is always directed forwards : when speeding a bit, a glimpse down at your stuff (bike computer, bottle, gears, etc.) means missing a whole frame of potential danger, and of course there is almost no landscape to look at on the sides because well, outside of the small area I light, everything is dark; on top of that, since I discover obstacles late, as soon as the roads goes a little bit downwards, I tend to stay with my hands on the lower bar (road bike) to be able to break or better handle the bike if I need quick reaction; so, all together, my neck is always bent 'backwards' to look forward; in that respect, I reckon it would be easier to use a bike that is not a road bike, the position would be more upright and watching forwards would be more natural;
6. one last thing: city (or village) street lights are fine for a pedestrian, but when riding a bicycle, I found them terrible, it gives the same lighting atmosphere as this type of twilight when you can't see anything clearly (I don't know how to say in English, we say 'between dog and wolf' to describe that confusing kind of crepuscular light where there is still a bit of light, but you can't tell a thing from another) but with extra lighting irregularity on top of it, while rendering your bike light useless.

Overall, my personal experience is quite opposite to the experiences I had read before: not so much peace and relaxation for me. Except when going up, when my speed is low, but then this is switching to another kind of suffering :-D

PS: ah, and there is also the question of clothing. I found it rather difficult to judge what to wear when leaving home; the cold of the night (and the temperatures which will probably drop as time goes) versus the heat of the effort. On the other hand, I only practice leisure cycling, which means that before I started riding a bit at night, I could almost always pick the day and generally the time of my rides, so that they were all sunny and dry and warm(ish) or hot, and I would typically go with a just a jersey (simply adding a vest for the morning start of 10-12 hours rides); someone who commutes or trains for competition is already used to plan for riding in shitty and changing weather & temperature conditions.