After further study: you can't save links privately via the Delicious bookmarklet anymore. I just clicked my "save this link" bookmarklet on an article I was reading (out of some nostalgic impulse), and I expected the usual interface where I could fill out some metadata and then submit it for saving -- but instead, the link was instantly saved publicly to my account, so I had to quickly click the checkbox for "this is private", save again, and then go to Delicious and edit it again to add the metadata I wanted.

Anyway, for people interested in an example of social listmaking done in a pleasantly focused way, Bagcheck is interesting to explore: http://bagcheck.com/ (recently talent-acquired by Twitter).