If I know the author's writing, or the person who wrote it.

The thing I don't like are cryptic LJ cuts that are the only thing in the post. So I click on "YEEEEE!" and find out that my friend has not encountered a spider in the shower, but is squeeing over some toy she wants to buy, with only the link to the toy in her post. That one bugs me.

I generally prefer cuts simply because it makes it easier for me to quickly scan the page, although a couple of teaser lines for a fic sounds like a good idea.