Interesting. For storing passwords I use Pass[1] which encrypts everything with GPG and then store it using Git in a private bitbucket repo. Works really well for me. I love the simplicity and ease of use.
One of the things that looked cool about blackbox to me was the support for encrypting the data with multiple keys and managing that.
I know some folks who use Pass and recommend it highly, but it seems focused on the personal use case like what you're doing.
I do still need to set up Pass myself, and was thinking about making an Alfred workflow to let me quickly access credentials. Does such a thing already exist? (searching for "pass" is not exactly effective :))
This enables you to control access per subfolder. You can keep your personal passwords in one subfolder and then have various shared subfolders. "pass mv" and "pass cp" will reencrypt with the gpg ids for each subfolder as necessary. You can also "pass init" an existing subfolder to add or remove gpg ids for existing files. See the man page for details [1].
[1]http://www.zx2c4.com/projects/password-store/