My main is a Prot Paladin. I did some raiding with him near the end of TBC, and he has been 80 for a while now and done lots of heroics and some raiding in WotLK. I don't claim to know everything about Prot Paladins, but I know a lot.
I rolled a new Paladin to keep as my Ret Paladin when I want to go along on guild runs of heroics and such and help train other tanks and whatnot. I know that I COULD respec my main, but I wanted to level a new toon and I love Paladins, so I started from scratch.
I was in Blood Furnace the other day and our group consisted of a Prot Paladin, 3 Ret Paladins, and an Enhance Shaman (who had about 500 spellpower and healed beautifully).
On one of the pulls, the Prot Paladin uses Hand of Reckoning but pulls a total of 3 mobs. He also didn't bother using avenger's shield but simply waited for the 3 mobs to hit his consecrate.
End result? Even after the mobs hit his consecrate, he had some threat on one mob, but almost zero threat on the other two mobs. He hadn't tanked much and failed to mark the targets. I paid attention and was hitting his main target that he had a ton of threat on, but one of the other Rets almost died because he attacked one of the mobs that had almost no threat from the tank. Through a combination of tricks and some good healing we survived.
I then gave the tank some suggestions as far as marking targets and thinking about building threat more quickly on multiple targets by either opening with AS on multiple targets or using AS as soon as he realized that multiple targets were incoming.
It seems to me that the new taunt could be somewhat hard to manage for a brand new tank. It is very handy for pulling a single target, but if that target has friends nearby, they are probably going to come as well, so it is very important to build threat on all of them in a group situation. If you are soloing, it doesn't matter so it might take a while to learn.
I also ended up teaching this new tank about line of sight pulls after we wiped on a pull where he threw his shield and then charged into a room that had casters....
I guess it is still good to do some BC dungeons while leveling up! Even though most WotLK dungeons are "Pull, AoE-Fest, Kill", it is nice to still have some training on stuff where marking targets, CC, and LoS are needed.