I used Opera mainly for the Unite feature now to be abandoned.
It is missing in v. 12. Some say its features will re-emerge in future extensions etc. Until then, Unite is still accessible in v. 11. Where do I get the v.11 deb?

P.S. In fact it seems that opera unite (at least in its older form) is dying while I am editing this question. Access to opera-unite applications from within opera-unite is poor or absent.

This issue is obscure to me for now (31.08.2012) because yesterday I have installed v12 in Windows OS (with opera-unite and basic applications - file sharing and media player - already installed) and it is still working (server is working). The v12 Ubuntu version came today without unite, and after installing v11 (which has unite) I could not get applications (file sharing, etc).

But they are still available: here and after downloading these files which have te .ua extension, they can be installed by opening them with Opera (v.11) But as opera-unite is no longer supported, it is possible that the server that provides the file sharing etc will soon be unaccessible.

Even if that is the case the question should maybe not be closed at it has a general usefulness independently of the unite issue.