When you have a large control hierarchy this can lead to very large rendered ClientIDs.
The following illustrates what is rendered when you have a label within a GridView row within a UserControl within a Repeater.
<span id="ctl00_ContentPlaceHolder1_SampleRepeaterWithDescriptiveName_ctl00_SampleWebUserControlWithDescriptiveName_GridViewWithDescriptiveName_ctl02_Label1WithDescriptiveName">Sue 1</span>
This can greatly effect the page size especially if the Repeater or GridView has a lot of rows.
One way to take care of this is to override the ClientID property of the control. Just create a server control that inherits from the WebControl. Override the ClientID and UniqueID properties. Use a hashcode of the string instead of the string itself.
Public Class LabelExtended
Public Overrides ReadOnly Property ClientID() As String
Public Overrides ReadOnly Property UniqueID() As String
The output using the extended label is much more reasonable.
<span id="-819157441">Sue 1</span>
This took a sample page from 381 KB to 138 KB. You can download the sample here.
I have a slight concern that the hashcodes may not always be unique. They probably will be unique in the string ranges that would be generated in this case. It might be better to use the hashcode generators found in the cryptopgraphy namespace.
I would be interested if anyone else has a better solution for creating shorter ClientIDs.