It sounds like pressure to give an answer very quickly. Just answer it later!

Agreed. I also don't think there's any problem to respond right away saying you will investigate the issue with a developer that day and get back to them. That way you satisfy the need to respond quickly so the customer knows "you're on it" while also being able to give a valuable answer sometime in the very near future.

I manage the Community team at SEOmoz, and part of the team's job is to do customer service via our social channels. We try to respond quickly whether we have the answer or not, to let them know we're working on it. It does help the community member feel like they're being taken care of quickly and that we're listening to them.

Cool, I've found the same when managing my community. There are certain bugs or features I say might not get addressed because we're rebuilding the site and prioritizing that over constant changes to the current site -- people are always appreciative with good communication. If a company makes a mistake, winning them over with customer service often creates an even stronger user/customer.