AG: I think I'll go with that. Ria gave me just about that same advice, and since the improv worked better than expected, I trust the advice a bit more than I did beforehand. "Hear me now, trust me later."
Strolen: I'll certainly keep the first part in mind. As for the second part, I was already intending to have it relocate it's 'lair', not only because it makes sense logically, but because the players told the town guard and gave them directions, so I've got a good reason to pull them back down there later. "We went to check up on your story, and didn't find any eggs or even a hint of a large creature living down in the sewers. Mind coming with us to make sure we've got the right place?" [Insert freak accident here, and cue Alien theme music] Muahaha.
@Ria, re: flashchat - I'm probably going to postpone the riot until a few days later, when they get pulled back into the sewers. Then I can insert all manner of freakiness on them, and have perfectly good extendability if the session goes longer than the last one (which lasted approximately an hour, not including character generation and a bit of 'setting the background' as it were).
Question for everyone: about how long do you tend to aim for with your sessions? What seems to be the optimal time, past which the players start losing interest? I've got the feeling at an hour is the bare minimum for a good session, since the players seemed close to disappointed when we ended. I'll probably aim for 2 hours next session.