Imp Shield Block is handy vs Vek'Nilash. Enough so that you should probably force the tanks who have it into tanking him,
By the way, -am- I wrong? Is there a situation where Prot is just nigh required?
Conc Blow is suprisingly useful vs stunable adds. (Noth, Anub, Sartura...)
The extra 5 seconds on shield wall are very useful, because they let you hit it BEFORE you need it, and still have it last through the entire duration of the effect you're concerned about (30% on huhu, Maex enrages, patch enrage, etc etc etc)
Shield slam is a lot of threat, and helpful in encounters with lots of taunting (ebonroc potentially) or encounters with deagros (broodlord, noth, Razuvious adds, vek'nilash post teleport when your rogues are coming in with combo points on the mob and cooldowns to burn).
This is ignoring the value of last stand, which is pretty noticable when learning stuff.
Prot is far from being a "bad" tree. While there are few situations where it is "required" (Flask of the titans will fix many many many ills) there are a number of situations where it's contribution to your progression is far more noticeable than any spec change in the raid. As a parting thought, If you are asking your priests/druids/paladins/shamans to spec for healing, and you are not fielding 2 protection tanks minimum, you are doing yourself and your healers a disservice.