Hooray! I believe openBC indeed gets it!
They now have a space where everytime you create a new contact, you can assign tags to the contact [ of course Christian from Visible-Networking beat me to the announcement – I only got to use the feature today – maybe because openBC has private releases or geographic releases phase-wise ].
And you can also search on the basis of tags under your “Contacts” page.
This is absolutely wonderful! Extremely useful!