Generally speaking, there's no better way to wind up a librarian than all the "sssssshhhh" jokes and comments about librarians. It's a stale cliché beloved of sit-com writers and journalists.
At my school we had a librarian who did think that silence in the library was important, so much so that she used to shriek and shout this belief as loudly as possible at five-minute intervals. She was an extreme example: but far from being "shushers", lots of people who work in libraries are themselves the target of complaints about noise. At the busy public reference library in London where I spent six years staff were regularly "shushed" by the public, never the other way round. And the phone! We were trained to ignore the phone if it rang while we were dealing with enquiries (we often had queues at our enquiry desk). John Major's Citizen's Charter suddenly turned this upside down - local government workers were commanded to answer the phone within so many rings, or seconds (interestingly, the party which believes in rolling back the state is actually quite keen on dictating daily detail to public sector workers - I digress). I am sure that Mr. Major's big idea was aimed at people working in offices, or that there was an underlying assumption that you would not be trying to answer the phone AND talk to people in person at the same time, but it didn't work very well for us. It did not come naturally to me to break off in the middle of an enquiry from someone physically present in order to let someone on the phone effectively jump the queue, and I hate it when anyone does this to me if I am at any kind of enquiry point or till.
On the other hand, how irritating the sound of an unanswered phone can be! S4C's drama Teulu, set partly in a doctors' surgery, perfectly captures the tense atmosphere created by a constantly ringing phone in the background. This noise (and we had two phones) used to enrage those who wanted silence in the library. I'm not sure what the answer to this one is, other than to recommend that those seeking silence should not choose to sit close to the enquiry desk - and to wish that staffing levels were more generous, so that you would not have frazzled people trying to do too many things at once and unable to keep up with the level of demand.
Another problem in the public library is that some really don't want to share the facilities. The internet seems to be full of people complaining about the very presence of children in libraries, for instance. It's a difficult balance to get right. Back in that reference library (a child-free zone, mainly), we did a (highly unscientific) user survey one year, and exactly equal numbers of the old and young complained about the other group's presence. Children and young people tend to get the blame for noise, but in fact older people can be quite noisy themselves ("old people coming in here to gossip with their friends when we are trying to study" was how one student put it). A public library is meant to be for everyone (and yes, children are people too, and the days of being seen and not heard belong to a bygone age); sharing usually involves compromise. My personal bugbear is mobile phone conversations in the library. You can turn your phone off occasionally, the world doesn't come to an end! Put it on silent and use texting instead if you really can't cope with being cut off from your lifeline for a bit! People using computers in the public library are particularly prone to this for some reason. "Hello! I'm in the library!" We know, we are also in the library!
In the university library we are a bit more spoiled. We try to manage noise by having different zones for different activities. There's the busy area around the desk, where noise is acceptable and expected, with the ringing phone and the enquiries. We also have an area in the basement, the e-lounge, where students can relax or use computers and where things not encouraged elsewhere in the library are allowed. We have other areas which are designated as silent study areas. The rarified atmosphere of a proper reading room (which is probably what a lot of people would still really like in their public libraries) is closest to being achieved in our Special Collections room, although we are cheating a bit in that it does not have an actual enquiry desk or phone, the source of most library noise, in its public area.
I have never ever shushed anybody in a library (a rude and abrupt way of communicating with people!). I have occasionally asked them politely to keep the noise down, and to desist from things like climbing on chairs and making general announcements to fellow readers, and I don't tend to raise my own voice unless something particularly unacceptable is going on: BUT I cannot do my job if I have to whisper at everyone or use semaphore. I can't whisper on the phone because the person at the other end won't be able to understand me, and I would very much prefer people with questions to ask them audibly and not whisper them at me at point-blank range. Talking to people, both in person and on the phone, is a big, important part of a librarian's job.