When you send a reply to a message that is sitting in your inbox, SpeedFiler prompts you for a folder. Once you've sent the reply, the original is still sitting in the inbox. You can very quickly file this in the same folder as the reply:
- Highlight the original message in the inbox.
- Press Ctrl+Shift+V, followed by Enter.
This works because Ctrl+Shift+V brings up the File In Folder window, with the most recently used folder already selected. This is the same folder in which you just filed the reply, so all you need to do is approve the choice by pressing Enter.