Today's standard feature that Opera is missing is copying rich text in a selection on a web page to the clipboard.
This is useful for selecting content on a web page, copying it and pasting it into MS Office, OpenOffice, rich text editors on web pages, mail clients that support composing in HTML and other programs that support rich text.
This works fine in IE, Chrome, Safari and Firefox.
Opera doesn't support this at all for regular web pages. Opera does support this partially if you turn an entire web page into a rich text editor by setting document.designMode to "on". But, that's not even close to the same as what other browsers support.
This is probably one of the most popular feature requests for Opera. Other browsers have had this forever. But, Opera remains broken in this area.
Some Opera users are against this though because they only want to copy and paste plain text. Well, the way it works in other browsers is that both a plain text version and an HTML version is copied to the clipboard. Then, which version gets pasted depends on what you're pasting into. If what you're pasting into supports rich text, the HTML version gets inserted. If you paste into a plain text editor, the plain text version obviously gets inserted. Further, programs that support rich text often give you a special paste option to paste the text version just in case you don't want the HTML version inserted.
Even with that in mind, some Opera users might want to paste into a rich text editor that doesn't have a special text only paste option. Or, they just don't want markup leaking into the clipboard for whatever reason. In these edge-cases, Opera could have an option to disable copying of rich text, if that's really necessary. But, other browsers and their users seem to do fine without that.
This is something that is not only a standard feature, but a required feature for a web browser.