Scenario:
You have wired up a link/button on the page with Page.ClientScript.GetPostBackClientHyperlink, passed it an argument and you need to retrieve that argument whenever the event is fired for the said link/button.
Solution:
In the event in question, you will want to put a check in to make sure that the __EVENTTARGET is the UniqueID of control in question and then you will want to pull out the __EVENTARGUMENT value form the request. Here are examples in VB.Net and C#:
VB.Net
Dim arg As String = ""
If Request.Params("__EVENTTARGET") = linkDeleteGoal.UniqueID Then
arg = Request.Params("__EVENTARGUMENT")
End If
C#
string arg = "";
if (Request.Params("__EVENTTARGET") == linkDeleteGoal.UniqueID)
{
arg = Request.Params("__EVENTARGUMENT");
}