Did you know, that in Opera you can give each bookmark (or folder of bookmarks), its own nickname?
That way, you can just enter the nickname in the address bar, hit enter and your bookmark (or folder of bookmarks) will open.
For example, when you are on your favorite website, press Ctrl+D to bookmark the website, click the Details >> button, and enter your nickname in the Nickname box.
You can also set a nickname on your folder of bookmarks. Just right click the folder (in the bookmark pane), go to Properties and then set a nickname for it.
Enter your nickname in the address bar, hit enter, and all the bookmarks in that folder will open.