I have two issues with the Novalith Cannons (and all superweapons, really) that are making the game unplayable for me:

1. (bug??) In a multiplayer game (2 human players, 8 AI) where I had a peace treaty with the other player, that player's novalith cannons (set to autocast) would bombard any planet I defeated and colonized, seemingly the instant I colonized it. The player was also at peace with the AI I was bombing, though I don't think it is relevant as on subsequent re-colonizations (after the planet had been bombarded and was colonizable again), the minute I would colonize it, another barrage of novalith cannons would launch. In essence, once the other human player got to scale with enough cannons, I was completely unable to expand any further.

2. (this has been the case since release) Novalith cannons and all super weapons state in their description (as best I remember) that they can attack "within a star system."  However, in multi-star games, they will launch attacks to other star systems, which travel at intra-stellar speeds. Thus, you may be well into changing the landscape of another star system to find your own super weapon attacks coming at you 30+ minutes later and wiping you out!