Gut feeling tells me San Francisco is vulnerable. Golden Gate Bridge the most likely target. Lots of tourists from around the world, too, makes it very high profile in the rest of world. My guess, though, is that any attacks will be multiple events in probably several cities across the country.
They wanted to do multiple state attacks last time,but OBL threw out that idea.They are less well coordinated this time,so I really doubt they can pull off a multiple state attack.