Threaded "bulletin board" conversations are rare to find anywhere anymore, at least in the places i haunt. It is very effective, in my opinion. Fb doesn't do it, so people have taken to @ing people so it is known about which comment they are writing. An "L"-shaped arrow can overcome the indenting troubles of more than 3 levels. Some nuanced conversations might need more than 5 levels.

All social networking need more options than just "+1" or "like". I agree (took me a while to come to this opinion) that "Dislike" is a bad idea, like feeding all trolls at all times. But "Interesting" is needed. If the post says "Hitler killed ____ people" or such, "Like" is hardly appropriate! "Funny" would be good, getglue.com has that. They have a drop down marked "Vote" which yields "Funny" "Agree" and "Cool". Not voting is plenty for indicating you find something none of the above. Digg.com's "bury" might have been a good idea there, since it's a numbers game.

I love the absence of farmvillemafiaelfvampire crap. But that said, there could be destination items that aren't annoying. Word games, just-for-fun contests ... some reason to go to G+ even when you have no notifications.

Discussions are already happening about how to spell things like "+1ing \ +1'ing" ... a good sign that G+ is taking off.