A thread at WMW flags a potential hijack problem with Google sitemaps. Someone more competant than I on the technicalities involved may like to comment.
Without giving specifics, there is a major problem with the site map system which allows anyone who can create a file to 'claim' ownership of a site, or a domain within a site.
If you own or run any WIKI, any system which allows user uploadable files (with specified file name), or any system which allows users to create pages with names based upon the title ('seo friendly' pages) then I urge you to take steps to ensure that URLs of the form:
cannot be created.