When I changed jobs last year, my previous boss was very insulted that I didn't tell him I was looking for a job and didn't ask him for a reference letter. (I did give him a month's notice when leaving.)
Is it usual or expected to notify your current workplace that you're considering leaving, and to ask your current employer to act as a reference?
If so, in what circumstances would it be acceptable not to do so? If it's not generally expected, are there any cases where it would be?
I suspect that this will probably be one that will vary a bit from country to country. I can only speak from my experiences in Ireland:
Exceptions to the first rule might include situations where you're a one-person team and you don't want to leave your current employer in the lurch. However, these truly are exceptions, and not the rule. In general, giving your employer an opportunity to replace you is what a notice period is for.
It is not expected that you inform your boss that you are looking for a new job, and it's certainly not required.
Look at it the other way:
Would your employer give you more than the minimum legal notice if they were thinking of firing you or making you redundant?
The answer to that is probably "no".
The notice period in your contract is there to notify your employer of your intentions to leave. In some countries/industries you get escorted from the premises as soon as you hand in your notice - for all sorts of reasons. These same reasons would apply when you reveal your intentions to move and if the move didn't happen then you'd be in an infinitely worse position than you were before.
In respect of a reference - in the UK all that a previous employer has to give is confirmation of the dates you worked there. So there should be no issue of not asking for a reference.
In a poor economy it would be inadvisable to quit a job before you have a new one. In a US state where you work "at will" they can fire you for almost any reason. You take the risk that they will let you go the moment you tell them you are looking.
This doesn't happen very often, but what does happen is that they can start to think of you as being disloyal or only going to be around for a short period of time. They won't send you to training, or add you to the new project.
Telling them you are looking does mean that in some cases they will offer you a raise, a promotion, or a transfer. Some times that is just a delaying tactic, and then they still view you as disloyal. In the end you may delay your departure for a while but ultimately you end up leaving.
You have no requirement in the United States to tell them, and little practical reason to do so.
Most companies you interview with will avoid getting a reference from your current company, especially if you let them know your current boss is unaware you are looking.
It isn't customary and shouldn't be expected to tell your employer that you are looking for a new job before you have one lined up. It is probably a bad idea because it can taint your image as someone who won't be around long if you don't find another opportunity and decide to stay.
That said, I can see why your boss might feel that way. As a manager it is frustrating to lose an employee who never communicated any complaints and just leaves without giving you a chance to remedy the situation.
You have to really trust your supervisor to tell them you are considering other opportunities before you have one in the bag. It sounds like you boss is a little disappointed that you didn't have that level of trust with them. However, it is somewhat of a catch-22. If you had that level of trust, you probably would be less likely to be looking for another job in the first place.
In the banking industry in the US, letting your boss know you are looking for another job can get you fired immediately. One bank I worked for monitored phone lines (and bathrooms) and if you were overheard to be looking for another job, the security department would have your boss and an armed guard at your desk the next morning to help you pack your things and leave. While this bank is an outlier, the doctrine of "at will employment" in the US means that giving your employer "too much notice" can result in you being fired.
In the US, 2 weeks notice is customary when resigning. It is reasonably common enough that when you give your notice that you will be immediately escorted from the premises, so that informing supervisors that you are "looking" can be very risky. It is my experience in the US that you should have all your personal possessions out of the office before giving notice.
