(In) Visibility

Scenario: A Datalist (or Datagrid), an EditItemTemplate, some textboxes control.
Imagine you want to have an hidden Textbox control now.

Don't use visible=false, if you want to get the text from the control

Instead do something like:

<asp:textbox id="MyHiddentext" runat=server style="display: none;" />

Your control will be hidden client-side, but it will be there for any request server-side