Yes please! Something like the "star" on google groups would do.
There is currently no way to do this: I was trying to use +1 for this purpose, until I realized that there is not way to recover the +1-ed posts.
And they're public by default, and I do not necessarily want to share what I haven't even read with the world!
This is, I think, a fundamental issue with G+
The result of this limitation is that I end up sharing things I did not even read, just to make sure I have a way to read them later: as I'm not, I guess, the only one doing so, it's just easier for posts to go viral.