I’ve just given a leaked release of Opera 10.5 Pre-Alpha a test drive and I must say that I’m very impressed with the changes I’ve noticed thus far!
I look forward to testing the Official Opera 10.5 Pre-Alpha release on Tuesday, December 22. However, until then I’ll be digging through this leaked version.
Note that Opera has officially warned against installing such leaked builds, stating that the official release will be “much better and you don’t risk getting nasty trojans on you pc.” 
Here are some screenshots I’ve taken. I don’t cover everything, but just enough to give you a good idea of what we should be expecting. I also won’t be detailing all of these pictures, but a picture is worth a thousand words right? Inspect them and see what you can find!
I did notice a lot of skin changes and a couple of bugs here and there dealing with the skin, but it’s overall very much improved. The internal “opera:*” pages also seem to be using a different style than previous builds, but then again they may have dropped using the Opera logo in the top of the pages.
Notice the border-radius support!
Try this build at your own risk!
http://rapidshare.com/files/323481638/Opera_1050_20192_in.msi
http://depositfiles.com/files/e01z2q5qp