See this question:
When should I use # and = in ASP.NET controls?
Summary from those answers:
There are a several different 'bee-stings':
<%@ - Page/Control/Import/Register directive<%$ - Resource access and Expression building<%= - Explicit output to page, equivalent to <% Response.Write( ) %><%# - Data Binding. It can only used where databinding is supported, or at the page level if you call Page.DataBind() in your code-behind.<%-- - Server-side comment block<%: - Equivalent to <%=, but it also html-encodes the output.
