Good question, David. In general, I think the two constructions are quite interchangeable. However "seems to be + adj" seems more immediate to me. She seems angry (often, or all of the time). She seems to be angry (right now; we should get out of here). Your cat seems hungry (she keeps trying to jump up on the table). Your cat seems to be hungry (you should give her some food so she'll stop bothering us). That's my impression. I'd be curious to see how others respond.

I like what Jordan offered however for me "seems + adjective" is more immediate and more popular in everyday language. At least within the circle of people I am in contact with.