This is actually somewhat amusing, especially considering our recent set of posts on escaping properties and items. We got a question over on our forums today that amounted to "how do I escape the percent sign in an item include"?
All escaping in MSBuild is done using HTML-style URL encoding. So, for the percent sign, you escape it by using "%25". This is how we escape the pre- and post-build properties, for example.
[ Author: Neil Enns ]