The "Web vs. Print" conversation has been dominated by two camps, each knowing one thing. One camp knew that the web couldn't replace print functions, and assumed the web wouldn't destroy the print model. One camp know that the Web would destroy the print model, and assumed that the web would replace print functions. Both camps were right about what they knew, and wrong about what they assumed.
Serious food for thought here and a very succinct summary of his very fine recent post Newspapers and Thinking the Unthinkable. And although Shirky was talking about newspapers, I think the general sentiment is also applicable to books and magazines as well -- with print journals already having been supplanted by online.
In terms of journals, if online hasn't exactly replaced all the print functions, I think that all the new functions added have, for most people, more than made up for what was lost. Print journals will disappear more-or-less completely in the fairly near future.
I think the same will be true for newspapers, that ultimately the added functionality that online gives will more than make up for the lost print functionality and that print newspapers will more-or-less completely disappear in the foreseeable future. Probably later than for journals, though I might be wrong on that.
It'll be interesting to see how that dynamic plays out for books -- whether online/ebook/Kindleish will add enough new functionality to make the trade-off worthwhile for the majority of people. I think it'll happen, it'll just take longer than for journals and newspapers.
(An interesting question: how exactly would you save something like Shirky's Twittering in Zotero or EndNote or something? As well, how exactly would you cite it in a paper? As a web page? blog post? personal communication?)