I just discovered a bug in my code for the MetaWeblog API getRecentPosts command - I was passing postId (which in this case is naturally empty) to the implementation method rather than blogId. So embarrassing. Lucky nobody was actually using it :-)
The updated code can be found here.
I discovered this one since I'm writing an implementation for my own web site which I'm currently putting through its paces.
Other than that stupid, stupid little slip it's coming on quite well.