But if there is a filtered entry for which I am not on the filter, I get that screen that says "Error: You are not authorized to view this protected entry." That screen doesn't have a "previous" button. I hate that screen. I can't get past it easily; I have to stop and go to an entirely different journal view. This is annoying enough when it's the journal of someone I don't know, or someone I do know who has known categories of stuff I'm filtered out of (private relationship issues, say, or inviting local people to parties I'm not local to), but when it's someone I know well who usually doesn't filter things in such a way that I can't see them, it's Just Mean (of LiveJournal, not of the person filtering). There are plenty of good reasons for me not to see things, but I would so much rather not know anything had been posted at all and just skip to the next entry I can read.
You see, I'm an information junkie. I need my information. LiveJournal informing me that there's an entry, and it knows what it is, but I can't see it, is like dangling catnip. I go into these horrible fits of curiosity, occasionally combined with angst of the "What if it's about me?! What if they're upset about something I did, and I don't know what it was, and they won't tell me, and then I'll do it again and EVERYONE WILL HATE ME ARGH!!!" variety.
These fits do pass, in time.
But man, I wish I didn't see those screens.
 Andres chimes in: "Did you know that the two most common links on the Internet are 'next' and 'previous'?"