What exactly does password hashing and salting protect against?

[eluser]wowdezign[/eluser]
It's true that if a person uses a weak password, then their account is vulnerable.

Hashing and salting passwords helps against "rainbow tables". I hope the reference is alright:

http://en.wikipedia.org/wiki/Rainbow_table

Some developers like to use a site salt. I use a different salt for each user in the db.

Hope that helps.