Unite was awesome. The problem is hardly anyone used Opera. A company like Facebook could actually do something with it. Imagine the possibilities for apps and games if a big chunk of Facebook users had it.
Unite is really awesome and I'm sorry to see it go, I used it for quick sharing with friends. Much more convenient than Dropbox when you just want something right there and then.
I think Unite suffered from not being open enough. You required an Opera account to use it, and there's no open specification for building compatible tools and services. What you could build into the browser itself was quite limited. (Plus you had to leave the browser open all the time, which can be a pain.)
It still does. The upcoming Opera 12 will not have it. The author makes a reference to the fact that the widgets have not been receiving proper attention since they were launched and need dusting off.
My point is widgets are (and have been) basically dead, at least in terms of popularity. I'm not sure Facebook execs are aware of their existence, so it's probably unlikely they have a future. Just have to wait and see.
The author doesn't seem to be up to speed. Opera has announced widget support will be dropped, along with Unite applications.
http://my.opera.com/desktopteam/blog/2012/04/24/increased-fo...
I guess this decision could be reversed if Facebook buys Opera.