Borat gives this an approval rating of great success!
Seriously, though, I had used the bolt-throwing Oxybeles and Scorpion artillery on occasion before, during field battles and some offensive sieges, but mostly the heavier stone-throwing lithobolos and onager for assaults on cities. However, it never really occurred to me the great advantages one could have placing an Oxybeles (or Scorpion if you're the Romans) inside your city while it is besieged by an enemy army. If placed at a reasonable distance and not obstructed by a building of any sort (and also well defended by a couple of your own units to fend against enemies once they get inside your city), enemy siege towers are totally screwed! The best the enemy can hope for is to use their ladders if they brought them, and to use the battering rams, which usually incur a good amount of casualties with boiling oil from city gates coming down onto the heads of those manning the ram and rushing in once the gate is breached. The funnest part, though, is waiting until the siege tower gets right up to the wall, with their soldiers piling in, and only then do you start hitting it with artillery bolts! By the time the enemy soldiers have reached the walls, the siege tower comes crumbling down! Killing well over a half of the unit if not upwards of 90% of soldiers in a single unit.
So awesome! I advise everyone to try it if they have enough money to recruit and maintain some artillery pieces in a defensive fashion, not just on your offensive campaigns.
Anyone else have success with this? And not just any old success: great success. It nice.