My thoughts are mostly on the irrelevance of ones Cutie Marks and how irrelevant they seem to be on a whole, and are rather just a small aspect of the ponies themselves. For example, Rarity's talent is Gem Finding. Mind you that is far from any one of her defining characteristics, and her living is made by fashion, which is supplemented by the finding of Gems, but really that just helps her cut out the middle man.

Applejacks special talent is something related to apples, I haven't really pieced exactly what together, but yeah. However she is highly praised mostly for her athletic ability other then some apple related ability.

Twilights talent is magic, yet she is also an encyclapedia of all sorts of information ranging all sorts of topics, and clearly shows superior management and organizational skills then all the other ponies.

I know Pinkie Pie has her own theory on her cutie Mark, but she's crazy and any story she tells should be taken with a grain of salt.

Though in case of Fluttershy and Rainbow it seems pretty consistent.