The Subtext team released version 1.9.4 (Windward) on Monday. I'm proud that my implementation of sitemaps is included but I must tell you - it's broken. Last minute change described in Simone's post actually makes sitemaps useless with Google:
The final release have just one small difference: the sitemap is inside a "sitemap" folder instead of the root folder of the blog, so the final url will be http://blogUrl/sitemap/sitemap.ashx.
But Google demands that the sitemap file is in "highest level directory you want search engines to crawl, generally the root". With this change this is not the case.
Until guys figure out what to do (release a new version, release a patch,...) Barry has a solution for you.
If you run one blog site - you basically need to change the web.config file to
<HttpHandler pattern="Sitemap.ashx" type="Subtext.Web.SiteMap.SiteMapHttpHandler, Subtext.Web" handlerType="Direct"/>
I hope the lesson is learned - NO last minute changes anymore, please, guys. You shoot yourself in a face soon or a later. I learned that the had way (multiple times)... :)