CCL is used locally for two reasons 1) error messages are better and 2) it ensures that we're writing portable code. SBCL is used in production because it's much faster and it's constantly being updated, so we get cool things for free. I have been eyeing lispworks but I don't know that it offers much benefit right now. We do plan on mobile apps at some point and that's a conversation we'll have with them.
Production itself is pretty much just a live image, not much different than what you'd have when you're developing. We use slynk to be able to connect to it and play with the data. Can see that here [0].
GC hasn't caused an issue yet. I imagine we will run into issues latter half of this year when we roll out alerts but those are challenges which can be overcome. That might even be a lispworks thing honestly.