Let me make it simple for you guys.
When Ale is fit and in form- 4-3-1-2
When there is no DP, or he is not in form- 4-3-2-1.
Any questions?
look at this assuming we have most of players available:
4-2-3-1
----------------buffon------------------
zebina---canavaro-CHiellini--Grosso
----------Sissoko---melo--------------
camoranesi---Diego-----Giovinco----
------------David-----------------------
4-3-2-1
----------------buffon------------------
zebina---canavaro-CHiellini--Grosso
---Camoranesi---Sissoko----melo---
------Diego-----Delpiero/Giovinco---
-------------David---------------------
4-3-1-2
----------------buffon------------------
zebina---canavaro-CHiellini--Grosso
Camoranezi---sissoko----melo------
--------------Diego--------------------
----------David---Delpiero-----------
There is a little difference there, we don't really know which formation are we using, cos either we playing camo as three man midfield or as offensive midfielder he is still going to do what he always do, so for Camoranesi is not going to make difference, same goes for Delpiero, he is always behind the striker. Someone mentioned that ferrara was not lucky with injuries that is true.
You could correct me with sissoko and melo they could be rotated. the rest in any formation the will play same game, fact the Alex will come back will make it easy for Diego... But if we have all those players in disposal we don't really need a formation just put them on the pitch and let them do the job without much complication. So when you see at bigger pictures 4-2-3-1 and 4-3-1-2 don't differ at all!