I'm new here, but thought about this and tried it today (after reading so many fun smoothie recipes.
I made my smoothie (usually skim milk, protein powder, banana, (sometimes a little peanut butter) and ice . . . but this time I added a TBLSP of instant fat free banana cream pudding. I put it in at the end after everything else is whipped up.
It seemed to add just a little bit of thickness to the smoothie that I felt it was missing.