Just like in FO3 I regret getting Animal Friend. The wasteland just isn't as fun without angry Bighorners charging at you, ya' know?
I loved that perk in Fallout 3 simply because random annoying mole rats and stuff attacking you while you are trying to enjoy the game, well, was keeping me from enjoying the game. I couldn't wait to take that perk. In new Vegas I don't think it is worth it. In Fallout 3 you got a perk every level, so i could afford to "waste one" on animal friend.
The perk I regretted taking was confirmed bachelor. Against people, that extra 10% damage isn't really needed. Now, if I could take a perk that deals an extra 10% to abominations, that would be nice. Confirmed Bachelor and the female version are a true waste there are only like 3 to 5 places in my entire Prima guide book that even list opportunities to use these dialog options, and they already have a speech check assigned to them as an alternate anyway. Also, they are the "homosixual" perks. I am not playing as a homosixual. They all involve flirting with the same six. The Lady killer and Black widow are no different. They are rarely used at all in the game. You pretty much take them for the minor damage increase.
Seriously though, when the human with the highest health is only 225 and the best non-energy weapon guns deal 100-120 damage, you only need to shoot them twice anyway. Also, if you are using a 20-40 damage gun with 100 guns skills and it's fully repaired, at best you are getting 2-4 extra damage per shot? It takes 10 shots to get one "free shot" worth of damage. With 10 shots on a 20 damage gun, you kill them anyway. The math just doesn't work for me. Again, if you could get a damage increase to abominations that would be different. They pretty much "start" where humans end. Normal Deathclaws and others have 200+ health When you start dealing with those numbers on a regular basis, every point adds up. In short, that 10% is chump change in small numbers, which humans are. In large numbers they really start to add up.