Agree with Zinn and Stilhelm. I've played a prot warrior for years and loved their capabilities, even if it was a little challenging at times. With the changes in Cataclysm, however, I find I'm spending way too much time focused on gaining and holding threat at the expense of losing situational awareness.

Luckily I have a prot paladin alt which has now become my main. Pulling and holding threat (even with barely any hit or expertise) is fairly easy and straightforward as a paladin, especially due to the auto-smart capabilities of the avenger's shield which won't break existing CC's. Also both the Avenger's Shield and Hammer of the Righteous are "solid" threat generators with just a single strike, whereas I have to use multiple abilities (sometimes multiple times) to gain gain solid threat as a warrior.

Without a doubt, I'm extremely sad to give up my warrior identity and unique abilities (i.e. charge, intercept, etc) but on the other side of the coin, I'm absolutely loving my paladin raid support abilities such as auras, off healing, and raid wide dmg mitigation. For me, being able to off heal a healer and keep them up so that they can keep me up is a simple amazing feeling.

So like the others have indicated, if you want ease into tanking, I'd recommend a prot paladin rather than a prot warrior. The flip side though is that if you can learn to tank with a prot warrior, tanking with other classes will probably be pretty easy for you in comparison.