Well, the best example I know of is proposals to do opportunistic upgrades from HTTP to HTTPS, for example via a browser header in the HTTP reply. If the browser performs the opportunistic upgrade, and negotiates an HTTPS connection behind the scenes, and doesn't tell the user that the connection was served over HTTPS, then accepting a self-signed cert invisibly in this context makes the user no worse off than not performing the upgrade (and better off against an adversary who's not currently performing an active attack).

I forgot what the current status of drafts proposing this is. Amazingly, I found that Rohit Khare described a form of this mechanism way back in 1998 (so it's not a super-new concept).