I know I'm slightly late to the party on this, it looks like most of the discussion of, and experimenting with Google+ Comments happened last week, but I just wanted to let readers know that for the moment I have G+ Comments on and I'm trying them out to see how I like them as compared to the regular comments.
The biggest disadvantage I see is that if you don't have a G+ account you can't comment. I haven't really gotten a lot of comments on the blog, and I think everyone who has commented actually does have a G+ account but there it is. On the other hand, I think this also means that people can leave comments that can only be seen by a limited group of people, so a few people who don't like commenting publicly may find they feel a bit more comfortable commenting on stuff.
There's certainly also an argument to be made for not having comments at all (a friend of mine has made that argument quite well on a few occasions), but I'm not sure I want to go that far. This does help aggregate discussions in multiple places and could allow for some more interesting control of comments so I'm going to try it out for a while and see what I think.
I really like the idea of comments form Google+ Posts about this post showing up on the blog, and being able to respond to them in either place. I'm not totally sold on some of the weirder idiosyncrasies of the system (people being able to leave comments I can't see and other weird stuff like that), but I imagine some of these will get worked out soon, and others may simply require a rethinking of what comments are or can be.
If you have any concerns about this (maybe you're a regular reader but don't have or want a Google+ Account, or maybe you just don't want to use that for commenting etc.) feel free to let me know via e-mail (should be in the "Contact Me" section of the blog site).