1) Main Tank Spec for guild progression - 80% of the time I am tanking Ulduar progression
2) PVP Spec. Prot is actually really fun in arenas. - 15% of the time
3) PVE Ret offspec. 5% There are some bosses in Ulduar that really truly only need one tank.
Respec's arent expensive. I used to blow 250g a night in sunwell in respeccing, when that was a lot of money (back in my day....) I have just fallen in love with hotswapping specs and having my bars good to go. It makes life so much easier. Glyphs however are pretty expensive and usually cost more than the respec.