Saving partial state of an ASP.NET control

Rick Strahl has a created a great control that's specialized in saving other control's state. This enables you to declare what properties you really care about, which is a great improvement over ViewState and even ControlState.
There could certainly be a few improvements, but check it out:
http://west-wind.com/weblog/posts/3988.aspx
UPDATE: Rick did actually improve his control based on the feedback he got and now it looks perfect:
http://west-wind.com/weblog/posts/4094.aspx