I have been running YSlow against my site and the Microsoft Ajax files are quite hefty:
http://ajax.microsoft.com/ajax/3.5/MicrosoftAjax.js = 99.3k
and
http://ajax.microsoft.com/ajax/mvc/MicrosoftMvcAjax.js = 136.7k
Is there likely to be a minified version of these files on the Microsoft CDN soon?