Robert McMurray of Microsoft just posted an excellent
blog post on how he provided custom FTP access for end users of a
BlogEngine.NET website he hosts for his friends.
The key issues are twofould:
1) User accounts on the website are not Windows accounts on the box so by default accounts on the website do not have FTP access.
2) The directory structure that he wanted the users to see did not map to the directory structure on disk, he wanted "virtual" directory structures (think libraries in Windows 7)
He implemented a custom FTP provider that uses the credentials (user name/password) from the CMS to allow FTP access for users of the CMS to upload files.
While his solution does require specific versions of Microsoft Software on the server (FTP 7.5, Windows Server 2008 etc), and would not play well in shared hosting, it is simple and elegant.
My thoughts are that this would be ideal for people running Orchard on dedicated servers who want to allow their users FTP access.