Are you talking about the goal away to Switzerland in October 2003? I've done some reading up on that Swiss game, and the build up to it.
O'Shea wasn't part of the preferred centre-half pairing at the time. It was Breen and Cunningham for the vast majority of the campaign. O'Shea had been the starting left full in the qualifiers under Kerr until that game and wsaplayed there because Kenny was suspended after a second yellow in the previous game VS Russia.
In that game, there was no clear leader in defence. One of Cunningham's greatest assets to the side was his organisational ability. Beside him, successive partners in Breen and O'Brien produced excellent performances. He told them where to go, where to stand, who to mark, who to track, etc. Without him, the frailties of both players were exposed. Breen was a fantastic servant to the jersey, but he was no leader, and O'Brien's performances dipped after Cunningham's retirement when he was expected to fill the organiser role. IMO he only really returned to previous heights when Dunne returned to the starting XI as his partner.
According to all reports, O'Shea was clearly at fault for the opening Swiss goal. He never really recovered after a slack pass to midfield let Frei in for a clear run at Given. According to these stats from the telegraph -
http://footballstats.telegraph.co.uk...e=career#stats - O'Shea's completed an average of four out of five passes in the past 3 seasons. For an even more recent comparison, according to the chalkboard on the guardian's site -
http://www.guardian.co.uk/football/chalkboards/ - he completed 65 of 70 passes in the last game against West Ham. Obviously this is an aspect of his game he's worked on and improved in the past 5 years.
As has been noted by other posters, the improvement in central midfield during Trapattoni's reign has been probably the most noticeable change in how the team is laid out. The two central midfielders tend to sit a little deeper than under previous reigns, but this allows the defence to make shorter, simpler passes, instead of having to aim for the half way line.
As a partnership under Trapattoni, Dunne and O'Shea have only conceded 4 goals in 6 games, and only 1 in 3 competitive games. In the last 2 home competitive games, a grand total of zero goals have been conceded.
Trapattoni has started them in the last 6 games in a row, barring injury or suspension there's no way he's going to change the partnership unnecessarily.
Going back to that Swiss game, with Cunningham suspended, O'Shea was moved in from left full (as he had been in the previous qualifiers) and Harte was restored to the full back berth. In effect, Kerr made two changes to the side when only one was needed. He made the same mistake against Israel two years later, and I've posted my thoughts on this before. I haven't seen enough yet from Trapattoni to suggest he's going to make the same mistake.