I have 38 Hit rating and it's only an issue where add pickups are needed, for which you can glyph an alt tank spec. Capping Hit rating is not a major concern for prot pallies. Survivability is. Check out the maintankadin website for more info.
Hit rating is VERY important for Protection Pallys. While we do have certain levels of passive threat generation, to tank effectively you must hit the target. Hit rating is one of the top 3 stats that need to be capped.
Melee = 8% or 265 to cap.
Also, our taunts are based on spell hit rating, which to cap is 17%. It is not viable to reach this as the resulting gear stats would prohibit our other abilities. You can, however, get the "Glyph of Righteous Defense" which adds an additional 8% to the chance it will hit. It gets you very close with that and it is a must as far as I'm concerned.
Hit rating is only decent for burst threat. You shouldn't worry about it whatsoever. You should never gem for it and shouldn't worry about it on your gear unless you are building a threat set and it's hit or expertise. Any fight that requires you to taunt consistently is a fight with no adds so it's safe to use RD and Hand of Righteousness so you have two taunts and the odds of both missing even without any hit rating is minimal.
hit rating for a pally really isn't a priority stat. as long as your over about 4% your fine. even if your worried about threat generation expertise is a more important stat to go after. but with the current set up threat is not an issue for tanks, unless the DPS you run with out gear your considerably.
the 8% hit is nice to hit, and for prot pallys (well mine at least) also have plenty on hit for their spells, i downloaded rawr a few days ago and it has my spell hit at 91% and my melee hit at 96% i think, so to stack hit for ur spells is usless.
expertise is much better, 24 for the soft cap and the Glyph of Seal of Vengeance is a must as i see it if u even just hit 20 expertise u will be fine, hitting to target is one way to get threat but to hold it u need expertise. cant have one w/out the other