Okay, I think I have to publicly eat a little humble pie here. I have spent the past several hours surfing WestLaw and Lexis reading opinion after opinion related to matter at hand. And this on my day off, too. The result: I'm changing my opinion from "clearly unlawful" to "possibly unlawful, due to changing circumstances." Let me explain.
The best source on this, I think, is still Justice Stevens's majority opinion in Sony v. Universal City Studios, 1984. In it, the justice wrote:
"Moreover, when one considers the nature of a televised copyrighted audiovisual work, see 17 U.S.C. s 107(2), and that timeshifting merely enables a viewer to see such a work which he had been invited to witness in its entirety free of charge, the fact that the entire work is reproduced, see id., at s 107(3), does not have its ordinary effect of militating against a finding of fair use.
"This is not, however, the end of the inquiry because Congress has also directed us to consider 'the effect of the use upon the potential market for or value of the copyrighted work.' Id., at s 107(4)."
On the subject of harm from noncommercial use, he then goes on to say,
"A challenge to a noncommercial use of a copyrighted work requires proof either that the particular use is harmful, or that if it should become widespread, it would adversely affect the potential market for the copyrighted work. Actual present harm need not be shown; such a requirement would leave the copyright holder with no defense against predictable damage. Nor is it necessary to show with certainty that future harm will result. What is necessary is a showing by a preponderance of the evidence that some meaningful likelihood of future harm exists."
Now we're getting to the heart of the matter. In 1984, the respondents were found to have failed to carry their burden to demonstrate actual or potential harm. Instead, they relied on the idea that home recording crossed an "invisible boundary," and that "the copyright owner has lost control over his program." In the absence of any reasonable expectation of potential harm, the Court had no choice but to find for the petitioner, overturning the lower court's decision.
The situation today, however, has changed. More and more television programs are now being released on DVD, to profitable sales. At the same time, technology has progressed to the point where the average consumer has, or has ready access to, equipment to make perfect recordings of digital broadcasts (where "perfect" is in the sense of being an exact replica of the digital broadcast, not a replica of the original master recording). If you gave me a copy of your entire collection of "Alias" episodes, digitally recorded straight from the antenna, you would be eliminating my desire to buy "Alias" on DVD, or a similar subsequent medium. The actual harm to the copyright holder of your sharing with me is nil, but the potential harm is measurable. Multiply that by the number of users of such technology, and you've got a problem.
However, 17 USC s 1008 specifically states that no action can be brought over the use of a digital recording device. In other words, you can make all the in-home recordings or copies of recordings you want. Whereas Sony v. Universal established the legality of time-shifting, the Audio Home Recording Act of '92 (which became Title 17 chapter 10) established the legality of space-shifting.
The problem arises when you provide a friend with a digital copy of a digital recording of a television broadcast that could, potentially, have market value at some future time. If I were to record "Alias" on a D-VHS deck and then loan or give you the tape, everybody would be happy, because there could be no potential harm from future sales by the copyright holder; it is effectively "time-shifting by proxy," as somebody else in the thread has said. But if you email me a copy, then you are distributing not the lawful recording itself, but a copy of that recording, and there's a good argument there to be made that that sort of thing causes harm to the copyright holder.
This is an open question; the advent of digital TV and digital recordings of digital TV, and the recent popularity of re-releasing old television programs on prerecorded media have changed the landscape a bit. Because the potential harm to copyright holders is small-- if it's present at all-- chances seem good that this will never go to trial. But if it does, I'm not entirely sure which way the Court will go.
If I were deciding it, I would have to say that sharing copies of home recordings does, in fact, present a potential harm to the copyright holder, and is therefore infringing. Sorry to say it, but there it is.
If we want to avoid having a court tell us that this is illegal, though, the best way to do it is to refrain from the practice. If you want to share digital recordings, burn them to DVD and erase them from your computer, then pass the DVDs around. That should be entirely lawful. Sort of... um... contrary... er... to what I said a few hours ago. Ahem. Oops.
The main point of my original post still applies, though: even if the act is technically unlawful, the damage done to the copyright holder would be so trivial as to hardly justify the cost of pursuing an action against you. That's not advice, just a little reality-check.
I think the real point here, though, is that everybody here wants to obey the law-- if for no other reason than to simply avoid unpleasant or inconvenient consequences. So it's just a question of determining exactly what the law says with respect to this sort of activity, so we can be sure to say on the right side of it.