Great tip, thanks...
But still not working...
<asp:Label ID="Label1" runat="server" Text='<%= "Hello " + "World!"%>'></asp:Label>
<span id="Label1"><%= "Hello " + "World!"%></span>
Text property expects a string, and if the tag is not <%# %>, it will consider that a literal string; <%= Hello + World %> in this case. If you want evaluation on the front page, you'd need <%# %>, but that will require you to raise DataBind event.
One nice thing about <%# %> is you can put them anywhere... such as
<asp:Repeater ... DataSource="<%# SomeObject.SomeCollection %>" ...>
So you can actually assign data to controls without doing it in code behind. I prefer this method because it lets me see where I'm getting the data from.