There's an interesting article on a fairly simple way to improve the sitemap that DotNetNuke generates for you. It doesn't require any core modifications but does set page priority up in a way that makes a lot of sense while also not requiring much work.
DotNetNuke Sitemap Improvement by Equana Solutions
DotNetNuke: Improving the tracking and reporting of Ad Views and Clicks - Part I
Setting up SmarterStats against a multi-portal DotNetNuke installation
E-Commerce Discussion Points
Giving your IIS Worker processes a proper identity
SQL Function to Parse First Name from Full Name
Styling the DotNetNuke Form and List module