I'm ending my SmugMug account in July, and I'm gonna move the files somewhere better, probably S3 or a VPS. As part of this, I need to download the files.
Someone wrote a SmugMug uploader, and someone else adapted it for downloading, but I haven't found his his code.
Separately, someone made smugdump, another person made smugmug-sync, and another person made Smuglr.
There's also Smugmug-Get-Images, but that seems less pleasant.