I used statistics updates as frequently as every hour but for most systems that have some "slow/off time" over night then daily is plenty good enough. What usually ISN'T good enough is just letting auto update to the job. 20% mods can be a VERY long wait during which time significant amounts of queries get some bad plans.
Best,
Kevin G. Boles
SQL Server Consultant
SQL MVP 2007-2012
TheSQLGuru on googles mail service