users get points when they log in as long as their last log in was more than the specified interval previous.
issues:
- what if users log in every few hours, never reaching this interval? do they get rewarded less than the users who log in less?
- if we save the time the login points were earned, where should we save this value? (there's no place in the userpoints table for a type-specific timestamp... add a column or add a new table?)
