Hello Ingo,
I really like Your google sitemap module. In combination with order SilverStripe measures like clean URL's sites easily rank on high positions without much effort.
For our ecommerce module SilverCart we need product detail pages to appear on the google sitemap. The thing is that our products are in fact DataObjects an not Pages. I had to decorate the function Items() of the class GoogleSitemap to make this work. I had to add the line
$this->extend("updateItems", $newPages);
after line 95 to make this function decorateable. I would be happy if You could add this line to the codebase so that I do not have to change core files.
Thanks,
Roland