Elaine Kennedy and Lee Spencer have studied the egg localitites in Argentina. Their study has led them to conclude that the eggs in the South American locality occur in lag deposits in channels, possibly cut by fluvial or sheetwash conditions. They have presented this at the Geological Society of America annual meeting a couple of years back in New Orleans, and the abstract is published (Kennedy, Elaine G. and Spencer, Lee: "An unusual occurrence of dinosaur eggshell fragments in a storm surge deposits Lamargue Group, Patagonia, Argentina. GSA Abstracts with Program, Vol 27, p A-315). There was no objection to her conclusions at the talk, so I think nobody was particularly surprised by the revelation. In this case, the eggs and egg fragments were clasts rather than being in nests. This of course is probably not the case where "nest" geometries would indicate otherwise, but is a qualifier to other studies which have been superficial in determining the nature of the eggs and the surrounding sediments. There are instances in China that I feel are fairly unambiguous in this respect, but I am not personally familiar with the stratigraphy there.
2010 Arthur V. Chadwick, Ph.D.