If you use Apple’s Mail.app for your email, and you’re sorting things into folders, you should definitely try MailActOn: it’s a free add-on to Mail that lets you create email rules and assign keystrokes to them.
Instead of dragging a message to a folder, you can create a rule that will put the currently selected message(s) into that folder, then hit “~”, and your shortcut key, and the email message is filed. Much quicker than dragging with the mouse.