I'm not a copyright lawyer, and what I list below may just muddy the waters further, but here's a stab at adding some clarification:
1. I don't think it's considered copright infringement if you were to pass on a copy of the magazine itself to a non-subscriber.
2. If you make a photocopy of an article or issue that you have purchased/received under subscription and file it away for your own records, that probably is OK under fair use. But if you give it to a friend (or friends) for their exclusive use, and you keep your copy, you are technically in violation of copyright as I understand it. However, when you consider the frequency with which the act occurs, the high ratio of cost to litigate to receivable damages, and the animosity inspired in the consumer, it almost always makes no sense to pursue.
3. In the case of electronic/digital files, you would have to destroy your file and printouts in the act of or as soon as possible after forwarding it on to your friend if you intended to comply with the copyright. How many people are actually going to do that?
The act of making multiple copies through distribution is what ultimately costs publishers money.