At the first software job I had (94-97), every engineer was expected to do customer support on rotation. Typically it amounted to one day a fortnight. I found it to be hugely helpful, in particular the software we were building (Desktop GIS) wasn't something that I was going to use myself, so understanding what the users got hung up on was really helpful. We could also be pretty responsive, it wasn't unusual to just fix a bug either while on the phone to someone, or within an hour or so of getting off the phone, and then we could just dump in on our BBS and tell them to dial-up and download it...