I've been doing HH daily and a few heroics with my pally as ret (+ 4 ele shamans), I wear my prot gear (even sword+shield) when tanking and it works out ok. The pally does take more damage but not significantly more, his threat gen is still decent but I do start out a bit "slower" on my shamans. Of course my pally has 14k unbuffed in his prot gear (15.5k when specd prot), I thought mana would be an issue but its not with 3 stacking mana totems and all the mana-returning attacks ret pallies have.

And of course its a helluva lot more fun running the pally solo in raids, kara, etc as ret

So yeah I'd recommend it, altho ret seems to be getting hit kinda hard with the nerf stick in patch 3.03