This is one I am posting for my own reference so I can find it easier... When Clicking a LinkButton in a Repeater, I needed the index available to modify a cached DataTable.
Situation: Getting the Repeater row index from the LinkButton
Solution:
LinkButton lnkButton = sender as LinkButton;
int RepeaterItemIndex = ((RepeaterItem)lnkButton.NamingContainer).ItemIndex;
Credit to kaushalparik27 at http://forums.asp.net/t/1333400.aspx/1