It would be useful if the destination filename on the master for FileUpload could be dynamic. At the least, being able to include the builder name would let different builders upload files without stepping on each other. It would also be really great to be able to include an SVN version number so that subsequent runs wouldn't have to overwrite files uploaded earlier.
It would also be nice if FileUpload didn't clobber the file in-place, but instead wrote to a temporary file until the entire file had been received, and only then moved the file to its final destination. This would avoid partial uploads being left in place and appearing to be complete instead.
Allowing the source filename to be dynamic would be handy as well, but at least that lack can be worked around by making sure the build steps always generate a file with the same name.