Opera 9 Preview 2 was released sometime last week. I have just downloaded it and had a play around with it and I am most impressed.
Perhaps the biggest change is Opera now has widgets support (a la OSX widgets). There's not many of them around at the moment, but the ones that are there look pretty useful. Searching from the widget on your desktop and having the result appear in Opera is now a possibility. They don't look too hard to develop either - there's a full tutorial on the Opera website. Also they have embedded a BitTorrent client with the browser, which seems like a logical step to me. I haven't actually used it yet though (don't use BitTorrent too much). There's also a very nifty content blocket which allows you to click on ads and then it makes blocks all images from that domain (although I think this may be a Firefox extension already?) When you cycle through tabs using ctrl + tab a thumbnail of each window tab appears (a la alt + tab in windows) which is very handy if like me you have anything up to 50 tabs open at the same time. There's also a feature that allows you to set cookie acceptance and CSS and other stuff on a per site basis.
All in all, it looks very good and shows yet more progression from Opera.