Do yourself a favor. The free version is more than enough for anything that I have ever needed. Works wonderfully, and is very lightweight. I have mine configured to minimize to the tray if the minimize button of a window is right-clicked.
I have to agree with Paul, a "Minimize to systray" option would be nice. I know that the author and some other people think that a file transfer program like WinSCP has no place in the systray, but I think otherwise. I like to run WinSCP's "Keep remote directory up to date" mode. That sounds to me like a process that could run in background all the time with no user input and outputs to a log file. It would be nice to have it run as a service, but in the meantime it would be nice to have a "minimize to systray" button.
By the way, this is a really nice piece of software... I tryed other tools to backup "My Documents" folder to my server and this is the one that works the best and is the easiest to set up. It's really easy to set it up to upload to an SFTP server.