On the Google Operating System blog, there is an entry describing 10 features that are only available to Opera users. Most of these features are helpful in everyday browsing. Like the entry says there are Firefox extensions to make the browser more capable, but all of these features are included with Opera out of the box.
I will just list out the 10 features, but check out the blog entry for more information. So the 10 features are: duplicate this tab, go to url, reload every 30 seconds, fit to window width, rewind, nicknames for collections of sites, tab closing, instant back, page zoom, and crash recovery.
There is also 5 other tips to check out if you are an Opera user.
