Peter's hit the nail on the head. Officers who are of the same rank and know each other will use first names and nick names when in an informal situation (Regiment dinner, SQN bbq etc). But this is never done in front of the ORs (other ranks) and usually not in front of higher ranking officers.
It also depends on which area of the Army you're talking about. For instance, the Special Air Service Regiment usually have a distinct lack of respect and concern for military procedures, and they're entitled to it, because they've worked damn hard to get where they are. This is not to suggest they are bad soldiers, which is definitely not the case. Hollywood would beg to differ, but SAS soldiers really don't have an equal in the international community.
Another instance that can change interactions between soldiers is war service. I've deployed to Iraq, East Timor and Afghanistan as a soldier, and in Afghanistan in particular officers and soldiers alike were calling each other by their names and nicknames etc. But having 107mm rockets and mortars fired into the base on a regular basis does wonders for relaxing military protocol. When we got back to Australia and onto base again, different matter, back to the norm, but in a warlike scenario, it's a little different.
As Peter said, it also depends upon which Army you're talking about. The Japanes Army are very formal and as far as I know don't tend towards the use of names or nicknames.
Anyway, hope this helps.