Membership Proivder and UserID for Foreign Key

I created a new MVC3 project in VWD2010.  It setup the Membership Provider stuff by default. 

I want to have the logged in user's "userID" stored as a foreign key in my own database tables.  I see the _LogOnPartial view refers to

@User.Identity.Name.  Would I just insert that into my own table (with no ref. integrity) or is there another preferred property/method?  Should I add a FK between the default Membership table to my own?

Thanks.