Are math grad students increasingly consulting SE and Wiki, ignoring research librarians and libraries, to their own detriment? Judging by posts and comments by graduate students in math.stackexchange.com and mathoverflow.net, I have come to the conclusion that a large part of their knowledge comes from SE sites and the Wikipedia, as opposed to traditional publications such as books and papers.
I was deeply shocked the first time I heard of a student researching the literature through Google, which spits out at least as many SE and Wikipedia answers as references to books and journals.  But, of course, nowadays I do the same, certainly more often than going to the library!
Are traditional publication forms becoming obsolete, in the face of purely electronic forms? Or, contrariwise, do younger people who ignore traditional forms miss out on essential information?
I think wikipedia is good for mathematics topics that are fairly settled. There are few errors and the ones that do appear (I've found some) tend to disappear quickly. You can get a good overview and if you follow up on the sources provided you can get a more complete view. So, I hope students use this for background on things they need to study.
But, by its nature, it is less useful to bring you to the state of the art: stuff that isn't yet &quot;settled&quot;.
I think SE is the opposite, in some ways. You  might find answers to contemporary questions, but the sources may be less reliable. Wikipedia has many editors (formal and informal) keeping things right, SE, less so and not everyone commenting really has a good answer. So, again, I hope that grad students use it when necessary, but with caution.
If the alternative is to set for ten hours at a time in a library, pulling older and older books from the shelves, it is no contest.
But reading things and being given answers isn't the best way to gaining insight into a mathematics problem. Not deep insight, anyway. For that you need to do some work yourself.
And, as you say yourself, it is a professional approach to use such resources. You do it yourself. And, I would say &quot;to the detriment&quot;, actually. It is a supplement and/or a place to start.