For the sake of a joke I'd place Fluttershy as Wrath, but I think the sin I'd actually, seriously ascribe to her is Sloth. She's often slow to act, and when she does act she usually does so incompletely. Failing to check with someone before doing something that they should have a say in, as in A Bird In The Hoof, is slothful, it's a way of cutting corners by excluding them in order to save the time, effort, and possibility of denial involved in talking to them. And refusing to act out of fear, as she did in Dragonshy, is also slothful.
Spike, I think, needs to be Gluttony, he always seems to be fixated on food.
Rainbow Dash is very obviously prideful, which... dammit, another sexuality pun.
There's evidence to call Pinkie greedy, particularly where it comes to her friends - she got pretty clingy in Griffon the Brushoff, and ten times worse in Party of One.
edited 29th Jul '11 2:35:12 PM by TurnwaysFlip
Nobody will see through my disguise... this time...