mailbox and public folder backup frequency

I appreciate this is very much organisation specific, but out of interest;

1) how often do you do full backups of your mailbox databases..

2) how often do you do incremental backups of your mailbox database(s)..

3) how often do you do full backups of your public folder database(s)..

4) how often do you do incremetial backups of your public folder database(s)..