Despite exiting the Rugby World Cup at the quarter-final stage, Ireland were the only team from the RBS 6 Nations who claimed a Tri-Nations scalp - Australia in the pool stages - with many of the squad returning with their reputations enhanced.
That came off a period of unprecedented success at both club and country level with a first Grand Slam arriving in 61 years in the 2009 RBS 6 Nations while Leinster and Munster between them have won four of the last six Heineken Cups.
All this is a far cry from a run of three successive Wooden Spoon finishes in the 1990s that culminated in a group stage exit at the 1999 World Cup.
The IRFU reacted to that slump by setting up of the four representative regional sides - Leinster, Munster, Ulster and Connacht - which has led to a closer coordination between club and country over demands placed on players.
And O'Callaghan - who has won all of his 80 Ireland caps during that period - was quick to praise his union for their foresight, especially when compared to the treatment of players by other unions.
"I think our period of success is down to the IRFU putting in place that we are all centrally contracted as opposed to being contracted out to clubs," he said.
"We are protected an awful lot more, our game management, how many games we play in the season, how fellas are coping with injuries and workload and things like that is all very heavily monitored.
"You just get the feeling that the IRFU are always really looking out for us.
"You hear horror stories about teams in France that inject guys and just get them on the pitch - that just doesn't happen here which is great."
New Zealand was O'Callaghan's third World Cup and at 32 his last chance of World Cup glory may have evaporated in their 22-10 defeat to Six Nations rivals Wales.
And while his memories will be tinged with bitter disappointment, O'Callaghan maintains he will treasure his World Cup experience.
"I think it was the first time I went to New Zealand and really enjoyed it," he said.
"I think that was down to the time of the year we were going, it was at the start of our season as opposed to the end of it. Normally you go there and you are carrying knocks and bangs and it's always a really bad time of the year.
"It was like we were New Zealand's second team for a while there, it was just great."
"The Wales defeat was hugely disappointing, because if you had told us before that we would be going out in a quarter-final against Wales we would have chewed your arm off, you don't get many chances like that.
And while that defeat may have brought the curtain down on his World Cup career, the 32-year-old is not yet ready to rule it another crack.
"You never know," he added. "Never say never anyway."