I mostly play my warrior in a group and I am a mostly protection build. I've tried other builds but contrary to the opinion most people seem to have, (maybe it's just sutification), I've found protection quite useful in tanking situations. Primarily the extra aggro generation skills:
Defiance -- This is a pretty clear advantage, you can create more aggro than usual here. Especially on things like shouts, which work an all engaged mobs, not just the one you're attacking, this allows better capability of keeping the 'side' mobs, the ones not seeing focus fire, stuck to you.
Improved Sunder -- This offsets some of the lack of rage generation from fewer fury talents than you would otherwise have
Also your single target aggro generation is much larger than otherwise. When I tried arms/fury, I had issues with not being able to keep up with rogues or hunters going all out. They'd have to hold back. If they got aggro, I'd lose rage from that mob, and have even greater problems. People seem to think protection is about defensive advantage, but IMO the real benefits to tanking come from the talents that give you extra aggro generation capability.
Personally, I did not find much use in Improved revenge, and specced out of that. Most things you really care about stunning regularly with revenge are things that are immune to stuns anyway. Concussive blow is very nice, but since they removed the Imp revenge requirement, I haven't had improved revenge.
Tactical mastery is very valuable, and I would get at least 3/5 even if you are protection. This allows you to charge in, thunderclap, then switch to defensive and still have a good amount of rage so you can demo shout or start sundering. It also allows you to swap out of defensive and execute, then swap back to defensive. And this was pretty key when we 3 manned Thermaplugg with 2 warriors and a shaman.
I have not found shield slam terribly useful except when soloing. It's like a mini-mortal strike, but in an instance, you have to sunder a bunch to keep aggro and to make the shield slam damage worthwhile (instance elites always seem to have exceptionally high armor). I never ended up really having enough extra rage for regular usage of shield slam. Generally sunder will do more damage in the form of increasing the damage done by others of my group (and this will be doubly so in your group where almost all of your damage will be physical damage). You may consider skipping shield slam if that's your intended grouping.
I also don't find myself using taunt enough to justify the 2 points imp. taunt. It's useful at times, but generally anytime where I need to use it more than just once as an OS skill, it seems like things are so bad that we would wipe anyway.
My build has me with deflection and 4/5 tac mastery in arms and cruelty, imp demo shout and piercing howl in fury with 31 points in protection. It's a pretty diverse setup, and while it's definitely gimpy solo compared to a MS warrior, it wasn't terrible to level with my build.
Other options for the leftover points include going like cookie cutter in fury with imp. demo instead of booming voice. or taking arms to anger management. Another tank in my guild has done that, and it is helpful in many cases where you want to wait a bit for someone to drink. If you take only 4/5 in 1H specialization, you can get both Anger Management and Piercing Howl.
Most people don't play with a consistent group. Before I played with my group I would have agreed with not really using Protection talents much. But now that I have a regular grouping, the extra aggro generation is noticeable. We can coordinate strategies which take advantage of the extra ability you have to hold aggro, which is something that was impossible in a PUG.
If you are really serious about your group, I'd stick with protection. If you break up, then spec for MS.
Starting leveling though, I'd start out with normal build orders. Spec to protection once you can pickup defiance and imp. sunder. The instances before 30 are downright easy for any organized group, and really it's not until about the level 40 instances that the protection talents start being very useful.