We can post polls, photo albums and private messages. How about a form? Like to do a survey or get some feedback etc. It wouldn't have to be to complicated, sort of like posting a poll. You have X number of questions you can ask. Answer fields could be text or when you pick a question you could choose whether the answer needed to be a boolean value ('Yes|True/No|False'), text or a number.
Of course, it would need to be controlled via the permissions like polls and photo albums to control what users could post forms.
Oh, obviously the field data would be stored in the db, and each user could only submit a form once. A area to page through submitted forms would also be needed.