See http://www.mbta.com/transitpolice/crimestats/ . Select Alewife. Bike Thefts have dropped from 28 last year to 8 this year (year to date).
That said it truly sucks when your bike is the one that is stolen. A ulock *and* a cable lock makes it less likely that yours will be that one.
The access cards to the cages now have to be registered. The problem is more that the cages fill fast.
You're not supposed to leave locks attached to posts.