i use the insidious big brother database (bbdb, a set of elisp scripts that runs under emacs) to track my contacts.

it integrates with vm (my MUA, which is also implemented in elisp and runs under emacs), so that i can type part of a user's name in the To: line of an e-mail composition buffer, hit tab, and it fills in the rest, including the e-mail address (which bbdb stores in a field named "net:" in its records).

i just tried to tab-complete a friend of mine for whom i lack an e-mail address, and i got the following error message in the emacs modeline:

only exact matching record unhas net field

i would love to use this construction in my everyday life, but i think it would unhelp people understand me.