It's looking like MetaWeblog API access is currently missing from Dotnetjunkies (and yes I did post a query on the forum).
I'd thought I might just be having trouble finding the right name and path, but then I managed to find http://www.dotnetjunkies.com/weblog/blogservice.asmx without any trouble, so that suggests that the MetaWeblog support hasn't been installed.
I don't know if it's still the case, but in the first official release of Community Server the Metablog stuff was an optional additional download that you had to install and configure appropriately - it appears that my horrified reaction at the time was justified: I reasoned that if it doesn't get installed automatically, often it won't get installed at all, which is bad news for blogging tools.
I'm now going to start looking at what would be involved in changing the support for Community Server in my mobile blogging tool (the previously mentioned embarrassingly named Diarist) to use the web service instead of a relatively standard API - this is annoying in that it will add complexity and code bloat, but apparently necessary.
Additional CS changever anoyance: I had to remove my PDC2005 flair,since the tag was too long to fit in the space allowed for it and therefore truncated, basically trashing the HTML in the links section.