Kelly has the biggest upside, while Rizzo is the "surest thing". Both are predicted to be in San Diego by the end of 2011, right around their 22nd birthdays. This trade also pushes Kyle Blanks, AGon's former replacement, to the outfield, once he recovers from Tommy John surgery.
I could barely contain myself today, seeing AGon being introduced and wearing a Sox uniform.
Fuentes could be the next Ellsbury, but he too is very young and I wouldn't expect him in the bigs until at least 2014. This trade really was about restocking San Diego's farm, not about competing in 2011 at all, and on that front I think the Pad's were successful.
That being said, Gonzilla is going to absolutely rake in Fenway.