Today's standard feature that Opera is missing is the showing of the I-Beam mouse cursor (cursor: text; in css) when hovering over text (even non-editable text) in a web page.
In browsers, the I-Beam cursor indicates whether the text on a web page is selectable and *or* editable.
All other browsers have supported this for years. Opera just shows the arrow mouse cursor.
Chrome and Safari support the I-Beam cursor even better. They show the I-Beam when selecting link text while Firefox and IE show the link hand pointer.
Edit: Opera 11.60+ has this now.
Some people are upset that there's no way to change it back to the old way though. Some also think that using the I-Beam for selectable text is wrong. In response to that, I submit:
This says it's for editable text, at least. But, it doesn't say that it can't be just for selectable text too. Besides Windows Explorer and IE use it for just selectable text.