I am also a customer interested in command-line use (for unattended backups). Unlike Pierre, I have been able to get the syntax to work as described in Win7. Boxcryptor brings up the dialog box if the archive does not exist (name wrongly typed, or not a complete path), but if everything is entered correctly it starts running silently and makes the Z: (or whatever) drive available.
But I would very much like to see a /quit command-line option to shut Boxcryptor down, equivalent to right-clicking in the system tray and choosing Exit. I have two different encrypted folders and sometimes need to switch from one to the other (I have the Unlimited Personal version). But if I try to run a second command, I get an error box saying that Boxcryptor is already running in the system tray. If I exit using the system tray then the second command works fine.
I don't need to use both encrypted drives at the same time, but there may be users who need that functionality. That needs more thought about the command line, since one would probably need /dismount and /add options. But for me, adding a /quit would be enough.
Otherwise, this looks like a really nice product - for backups, it is much more flexible than Truecrypt, which forces you to save the whole archive if even one file has been changed.