I'd also welcome such a functionality (database).
One of the possible uses I can think of is a collaborative dictionary/glossary, where the teacher sets up a database with fields like "word", "part of speech", "definition", "example sentence", etc. The students then fill up this database with new vocabulary/keywords they have encountered in the course.
Of course it might as well be a relational database, where one word could have several definitions (meanings), each meaning could have several example sentences, etc. However, this would be difficult to implement and might be too complicated to operate. I believe in 99% of cases a flat database would be just fine. The teacher can always create fields for "definition 1", "definition 2", etc.
I'm sure other moodle users could come up with more uses for a simple database module.
PS
I've known moodle for just a few days, but I think I'm already falling in love...