Limiting number of selections on multiple select

This is actually a question I had for D6 also.  Is there any way to limit the number of selections people can make on a multiple select list? - including one that is made from a pre-defined value.  I have a field called "industry" and have found that some people will select every value.  Is there a way in D7 to limit them to say 5 selections?  Do I have to mess with SQL to do this?