The feature is available on the work info page (card catalog page) for any specific book—yours or someone else’s. Here’s an example. At present, it only works for books, not for general works. (After all, a work may have 1,000 ISBNs under it.) We hope to extend this in the near future. The results aren’t saved in any way, so if you’re doing a bibliography, you’ll have to do some cut-and-paste work.
We’re linking to OttoBib because we think it was nicely done. But, down the road, LibraryThing may need a stronger solution—one that works with non-ISBN books and which saves and juggles citations, rather than just creating them. We have some ideas along these lines, but your suggestions are always apprecated.