Interestingly, the Greek word translated here as "greater," [ megas ], is translated another 150 times as simply "great." (In the kjv, anyway)JOHN 14:12
12 Verily, verily, I say unto you, He that believeth on me, the works that I do shall he do also; and greater works than these shall he do; because I go unto my Father.
In the summary of translations, this same word is listed under "12 misc" translations. ( translated as "loud" 33x )
This may seem a small matter to some, but the "-er" is what has our attention, and for some, that little suffix can mean that pleasing God is impossible.. after all, its hard enough just to be like Him and not have to worry about doing anything "greater."
I do agree with others regarding the Spirituals (gifts). Though I am convinced that it means we have to know, to accept, and to nurture that part of Himself that He blessed us with. However, we should not think of this "giving" as an ability, but as Him personally, dwelling in us and, (if we allow Him to be), working through us to to draw others to Himself. Understandably, some may be best fitted to the noble tasks of service to one another, rather than evangelizing the unsaved.
In whatever we are given, we must not focus on whether or not we can achieve these greater things, but that we should allow Him to work in us and be able to recognize what it is that He wants to do.