As you all are doubtlessly aware, Burbank-Bob Hope Airport is the only airport in the region directly served by rail. Metrolink and Amtrak both stop mere steps from the terminal. According to LAist, Jet Blue has decided to take advantage of that fact.
Your same-day JetBlue boarding pass is now good for a Metrolink ride to and from the airport. From what I can tell, that means "from anywhere in the system to/from the airport," but I'll edit this post when I have better information.
Sadly, JetBlue's main hub in the region is the Long Beach Municipal Airport. If you've never used it, it's a fantastic little airport- few passengers, short security lines, little delay- but it's one of the most difficult to get to on transit from the IE. Still, this provides some options for car-free travelers looking to get away.