This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
You don't need to memorize Roo commands. You can discover all the commands, by simply executing help command from the Roo shell.
Also, Roo provides TAB-based command (and argument) auto-completion feature. This means, you can enter the partial name of the command or argument, press TAB key and Roo will complete the command or the argument for you, or Roo will show you the list of matching commands or arguments.