Most impressive. I love to hear when bots learn new emergent behavior (wether programmed or evoluted). Especially group behavior, like my fish school bot. I just think it's the coolest thing bots can do.
I've rewritten most of the core routines (including reproduction) to be less chaotic and more centralized. As a result, they're a dream to maintain, and also incredibly buggy (any new length of programming always is). There's a bug I'm trying to isolate now that is driving me absolutely crazy. I can't seem to isolate it. As I step through the program it all seems just fine. If I let it go it screws up. I just can't find exactly where it's screwing up. Most infuriating.
On a plus side, when the program does something naughty, it won't just exit anymore. Or save your sim or anything like that. The engine will simply stop running, but the GUI will remain responsive, and you'd be able to (theoretically, I'm not this far yet) save the sim, attempt to restart, load another sim, etc.
A wonderous unforeseen consequence I am simply enthralled with.