But they know that reputation counts for nothing when it comes to the Heineken Cup and, despite the Ospreys going down 38-17 at Castres Olympique, they are expecting a battle royal when they run out at in front of a sell-out 10,300 crowd.
"You only have to look at the results in the Celtic League to see how the Welsh sides are improving. With the Celtic Warriors going out of existence, and their players being divided among the remaining four regions, the squads have become much stronger," said rugged international lock O'Callaghan.
"You need to have strength in depth to succeed in the Heineken Cup. You have to be able to cover injuries and be able to hurt teams off your bench.
"The Welsh sides will have international players among their replacements and will be far stronger than they have been in recent years.
"I don't think I've ever had an easy game in Wales and I can still remember the defeat we suffered against Neath at The Gnoll in the Celtic League in 2001. That was a really tough game and we got an awful hammering."
Munster gained their revenge in the 2002-03 Celtic campaign with a comprehensives 35-19 victory at The Gnoll and that 37-17 triumph in front of more than 30,000 fans in the final at the Millennium Stadium.
But the newly formed Ospreys hit back on Neath's behalf last season by notching a notable double in the Celtic League, winning 33-26 at St Helen's and 18-15 at Thomond Park. They have yet to meet this season, although the Ospreys have already beaten Ulster and Leinster and will have their eyes on an Irish hat-trick when they tackle Munster in the Heineken Cup.
"The Ospreys are unbeaten this season in the Celtic League and Gavin Henson and a few others are playing out of their skin. We know The Gnoll is a bit of a fortress and its great news the game is already a sell-out," said O'Callaghan.
"That's the appeal of the Heineken Cup and it's going to be another great occasion. When the Heineken Cup comes around it doesn't take much to get yourself up for the matches.
"There is a great spirit within the Munster squad and we always increase our work rate in Europe. We go into these games prepared to give every last ounce of effort. We're obviously proud of our record at Thomond Park, but we don't brag about it or take it for granted. If any team is better than us and beats us there then fair play to them.
"It is a very personal thing playing in front of your family and friends at a packed Thomond Park. If we didn't give our all then we wouldn't be able to walk down the street and look people in the eye."