Do good manners still matter these days?
I think that manners still matter in so far as they help to reduce conflict in social situations. For example, one might take the following as a general rule of etiquette 'avoid offending others unnecessarily'. It is fairly simple to see how following this kind of rule would 'smooth the social waters', so to speak, leading to more civil interactions.
Also, living in the kind of social setting you find in a city (or similar) you inevitably interact with a large number of people that you have never met before. When conducting these interactions you don't have a past relationship history to tell you what does, and does not, constitute appropriate behavior when interacting with these people. Manners can thus act as a rough set of guiding rules to govern these interactions in the absence of a personal relationship 'protocol'.
Have we lost the art of good etiquette?
I'm only 20, I can't really comment.
Are manners the mark of a civilised society or just a stuffy set of outdated rules?
Certainly, they seem to be beneficial (some reasons are given above) but I still think there is strong sense in which they are arbitrary. Take, for example, customs regarding greeting gestures, e.g. some men will not offer their hand to a woman to shake as a matter of etiquette, whereas they will readily offer it to another man. Similarly there are rules regarding the use and placement of eating implements in a restaurant. Rules like these strike me as highly arbitrary and should probably be regarded as unnecessary. More general rules like 'do not offend others unnecessarily', on the other hand, seem justifiable given the non-arbitrary social benefit they produce.
Note also that the latter rule I support (i.e. that we should avoid offending others) can be used to justify the pursuit of seemingly arbitrary rules, e.g. following eating utensil etiquette when dining with one's grandparents. While this may provide a situational justification for some of these rules I still think that the more arbitrary practices could stand to be rejected when considered outside of such situations.
Do/should manners be a feature of the workplace? Our relationships? Our home lives?
In line with the above, I advocate rules of etiquette which can be justified on the basis of their social utility alone (i.e. the 'avoid offending others' rule) whereas I suggest we should be able to pick and choose amongst the more arbitrary ones (unless, of course, doing so offends more central rules). I think personal relationships perhaps have more room for flexibility since the development of relationships involves some degree of negotiation of what is, and isn't, appropriate (though this 'negotiation' need not be explicit).
Are manners a generational issue?
For the most part I would say they are. As I have identified above, there are probably core, abstract rules (which perhaps align themselves more closely with what we would call moral principles) which persist through time, across generations. However, the bulk of any given system of etiquette/manners seems to consist mostly of prescriptions of the arbitrary form.
Also, some items of etiquette may once have served a social purpose only to have later become redundant. For example, in a society which uses left hands to wipe after defecating it makes sense not to eat or shake hands with one's left hand. However, once toilet paper, soap and running water are introduced there is little reason to maintain such a practice.
