I often need to update only folders that already exist, so when I copy from source to target, it must only copy folders that are already in target.

SuperCopy is just a (nice) wrapper for XCopy. If Microsoft adds that capability to XCopy, then SuperCopy will be able to do it too. By default, if you try to copy open files with Windows or XCopy, the entire operation will terminate once an open file is encountered. Super Copy keeps going when it encounters an open file, but the file doesn't get copied. However, Super Copy gives you a second chance. You can use the 'resume transfer' mode to go back and finish copying files after you have closed them. This takes seconds - compared to performing the entire transfer over again.

Do you think to add to SuperCopy an option to copy open files too?

I'd like to do that too... Unfortunately robocopy can only be installed via the resource pack, something that removes the convenience edge. Vista will have robocopy, though, and I hope to make a UI for it as well once Vista becomes predominate.

How about a UI for robocopy rather than xcopy?