I recently became aware of the System.Web.UI.WebControls.Localize control in a lab for the ASP.NET 4.0 MCTS certification course. The purpose of this control is unclear to me.
This described it best:
The Localize Control lets you localize any element on an .aspx page. It provides a design time feature not offered by its base class, the Literal control; in particular, the Localize control provides design time editing of static content so you can see a default value while working in page design mode.
Found at: http://wiki.asp.net/page.aspx/357/localize/
MSDN (bottom section has a good description)