Forms data resides in the database as long as you do not delete the instances in Forms. There has been talk in the future about possibly having a way to setup retention like schedules that would clearout data that is X amount of days old, but I don't know if or when that would come. If you are wanting it for reporting reasons, I would recommend what Aaron said and write it to an external table as you would have complete control over that table, unlike the Forms database.

Well we're already writing the data to an external SQL table for integration purposes but the client would prefer to use the Forms reporting tool for running reports on the data collected.  

We'll have them run a full report on all data points and save it to Excel at the end of each year so that they'll have the data easily accessible should it ever be removed from Forms but we'll also have the SQL table.

We just wanted to make sure there wasn't a setting somewhere that dictates the storage parameters of Forms tables.