Today's standard feature that Opera is missing is form autcomplete.
When you submit text fields in a form on a web page, IE, Firefox, Safari and Chrome all *automatically* save the values for later use for the web page. Then, when you type in that field again, the browser either autocompletes inline or shows a drop-down (that might be resizable with dragging) of your previously-typed text values where you can choose one to auto-fill the field. Further, in IE, Chrome and Firefox, you can press the down arrow in the field to bring up the list without typing anything.
Opera does have the wand for saving usernames and passwords. They're not auto-filled into the form where you can just click the login button for the form though. You have to invoke a keyboard shortcut, mouse gesture or click a button. But, that's consider an upside for some Opera users.
Opera also has the notes panel where you can save notes. In a form text field, you can right-click and goto "insert note" or just press the down arrow to get to the notes. Using this, you could put some common things you use in forms as notes.
Opera also has "Ctrl + F12 -> Forms" where you can predefine some auto-fill info for particular text fields that have a certain HTML name/type attribute. Opera will then support autocomplete, for those particular fields.
But, for all of those things that Opera has, it's limited and it doesn't support automatic autocomplete like other browsers do.