It sounds like they are referring more to deep linking into someone's site and bypassing what that site might consider to be the preferred way to get there.
It might relate to the early Ticketmaster case, in which that company sued Microsoft for linking to ticket purchasing info on their site. They were concerned that Microsoft Sidewalk would develop the user loyalty rather than Ticketmaster's own city entertainment offerings.
Framing is another issue, I'd say. I haven't seen case law on that, though it may exist. About.com still uses framing extensively.
I would avoid linking in a way that would really be confusing to the user and make him think the content he is seeing is part of your site. Even then, my guess is that if the site owner is offended they will let you know with a nasty letter before they sue you.