I'm so used to Control-C for copy, Control-X for cut and Control-V for paste that it never occurred to me that other options (such as the Edit menu or right-clicking) don't always work in web-based applications like Google Docs. Google Operating System points out this flaw, which is almost unavoidable because of browser security requirements.
Using the keyboard shortcuts in Google Docs works fine, but if you try using the edit menu, you'll see the error message above. I'm all for encouraging the use of shortcuts, but it seems odd to not support the option at all. Docs also blocks right-click options. The folks at Google Operating System got offered a web-app to fix the issue in Chromium, but that didn't appear for me in Chrome. It's not a major issue, but it's worth bearing in mind when explaining Docs to mouse-heavy users.
Google Docs and Clipboard Access [Google Operating System]