Sozlet went once without my knowledge -- that is, a friend's mom asked me if she could take her own kid and sozlet to a movie, I said sure, and then later I found out that she'd dropped them off at the movie, left, and then came back to pick them up later.
I was a bit surprised by that and wished she'd asked me first (it was all via email/ text so not a miscommunication thing, I went back and checked just to be sure), but no harm done so... <shrug>
That was maybe six months ago? (She's 11 now.)
Then just a bit ago a passel of her friends (like, about a dozen girls and then another set of about a dozen boys) went to see the Hunger Games together, but that doesn't really count because there were a couple of parents with the horde.
Whether I let her go on her own or not mostly depends on where and who she'll be with, I think.