From Declan McCullagh:

What does that mean for me?
Starting three years from now, if you live or work in the United
States, you'll need a federally approved ID card to travel on an
airplane, open a bank account, collect Social Security payments, or
take advantage of nearly any government service. Practically
speaking, your driver's license likely will have to be reissued to
meet federal standards.

The Real ID Act hands the Department of Homeland Security the power
to set these standards and determine whether state drivers' licenses
and other ID cards pass muster. Only ID cards approved by Homeland
Security can be accepted "for any official purpose" by the feds.