What does the castle validators offer me over standard data annotations?
I am a first-time user of xVal, data annotations and castle validators so there will be a learning curve regardless of which I decide. Is it worth it to just start using casle validators (I'm assuming they will be more robust)
We went with Castle validators because the validation attributes that they offered out of the box meshed better with what we were trying to validate than data annotations did.
Extending either is pretty easy so I wouldn't lose any sleep about picking one over the other. Play around with the two a little bit and see if one suits your general needs better than the other and then run with it.
The one ding that I will give to Castle is that getting the DLLs that I needed was more of a pain than I would have liked - I had to do a bit of hunting to get to a daily build that includes the validators.