I always get terribly concerned when someone deletes his journal. It always causes some kind of drama, too, from what I’ve seen.
I can certainly understand the need to take a break from LJ, or the net in general.
It’s very likely that you’ve said SOMETHING in the past that was meaningful enough to someone out here that we put it in our memories, or otherwise want to refer to it again later. I, personally, can only wish you’d just leave your words there. That’s a bit selfish, though—and I know quite well that words on the web are ephemeral.
If you want to move all of your old entries so that they’re not publicly visible, you can use a tool like HideJournal. (I haven’t tested it.) There are others, too—take a gander at lj_nifty. If you make them all friends-only or use some custom friends filter with nobody on it, you’ll have accomplished the same thing as deleting your journal. With less drama. And you’ll have more than 30 days to change your mind.