Here's some more info for you:
Digital Rights Management Issues
* Content from the Kindle Store: Books and other non-subscription items you purchase from the Kindle store may be downloaded to up to six Kindles registered to the same Amazon.com account. If you have exceeded your download limit, you must delete the item from one Kindle to transfer it to another. Subscription content can only be downloaded to one Kindle at a time, and only the seven most recent issues will be available for redownload in the Kindle Content Manager or from Your Media Library.
Someone posted on the Amazon forums that there is a round about way to share subscriptions. Subscriptions are identified with one particular Kindle when it comes to downloading via Whispernet. In order to share, the other person on the account without the subscription must go to the media library and download the subscription to computer then transfer it to their Kindle.
If the Amazon forums were easier to search, I'd link you. Instead, tomorrow I'll post and ask for confirmation and then post a link when I get an answer.