What Google Contact fields (if any) do you fill for your activities?

I have discovered that contacts from Google have a lot of built-in personal fields (not a promo). Birthdays, relations, skills, bragging rights (lol), and others — the whole dossier. What's peculiar is that some fields are featured in the API but not in the actual interface, as it seems.

Does anybody fill in manually / by other means at least some of the contact fields? Do you use Google Contacts at all?