Don't think it will have a key. FEAR/splinter cell were beta's if I remember correctly , they always have keys. BF2 is just a standard demo , can't see a demo having a cd key.
Would have to have authentication servers up , then supply tons of keys for magazines , or redo the demo for the free release. Seems like a lot of effort for a standard demo.
Just don't see it having a key myself , but we'll see when it gets released.