Exception #1: To add more intensity of emotion
Remodeling my house is really costing me a lot of money!
Exception #2: To describe a sudden change in behavior
You are being so horrible today! (Normally, you're a fine chum, but today you're a royal jerk!)
Exception #3: To describe a change in condition
His guitar playing is sounding better and better every day! (he's learning guitar, and it's getting better)
Exception #4: To make something more polite
We were hoping you could explain the problem. (We hope you can explain the problem is a bit more forceful)
Anyway, if you don't have a copy of Cowan's Grammar, you really should get one. I resented my professor for the fact that we didn't use this book too much in class, but I am still referring to that book in teaching any thorny issues.
All things aside, it conjures up a pretty funny picture if you say the soup is smelling.