Will this cause any harm? Does it serve any purpose other than tell browsers you have .net installed?
I like this article about changing the header to Pure Evil. Genius!
http://www.iishacks.com/index.php/2009/11/11/remove-x-powered-by-aspnet-http-response-header/
This header (and a few other headers) is not required or used by modern browsers and can safely be removed from the web site configuration in IIS without consequence. Other server-side languages also tend to include a “Powered by…” header that can be safely removed. Here is another article that claims the same thing:
https://web.archive.org/web/20210506093425/http://www.4guysfromrolla.com/articles/120209-1.aspx