Heh. I'd hardly call this a useless script. It's actually a pretty nice effect. I'm surprised it hasn't been done before (unless it has....), considering how visible and plentiful those things seem to be at night. Then again, we don't have those around my area, and maybe most people don't.
The effect looks great. I honestly was ready to look at the script and give you a ton of comments (based on my "expert opinion" after having only seen them a few times), but it looks awesome.
I do have a few suggestions, however:
1) Make the flies appear ALL around the player, not just in front of him. It looks pretty odd when I turn my head and don't see any behind me (let alone when using the command view).
2) Add a parameter to determine the frequency of the flies (the random delay).
3) Add another parameter that determines what object the flies will be centered on. This way an editor could anchor the flies around a specific area on the map, or could use the script during cutscenes.
4) Add a way to exit the script (via a global variable, or other means).
Also, one more thing. I thought fireflies (and I have heard them called "lightning bugs") were greenish? The ones I've seen were that color, at least. Are there different species with different colors or something?
Nice job.
EDIT
Ack! I just saw the 'bugs' up close, and they look terrible! I'd suggest you use the "kouleSvetlo" particle instead of the "cl_fire" one. It looks much nicer, although you might need to re-adjust the size and color of the particles.