Oh crap I know nothing about this yet. Well here's some random guesswork and half-baked opinions.
Circles looks like Facebook in that it's about sharing privately even though unlike Facebook you can put someone in a circle of yours without asking them. Whether they're listening or not when you share with that circle you can't tell, but this is true in Facebook as well. This is like asymmetric "following" model in Twitter but more private. Asymmetric relationships are exactly what the web is - links - and they are key to the web's scalability. You don't need someone's permission to link to their web site from yours. This is why Twitter took off so quickly, especially amongst popular people (including celebrity academics) who were swamped by Facebook friend requests. They can share and others can respond but they needn't hear the backchat except from people they follow in return.
Sparks looks like Twitter in that its about sharing to (or following) the world. I guess you can enter short spark updates somehow but its not clear. Anyway unlike Twitter (and Buzz) you follow interests that you enter not people. That's dumb. A person with all their variety and interests are far more interesting than search terms ever will be. But it's probably smart for Google in other ways.
Hangout looks fantastic but too good to be true. Getting real people to do multi-person video conferencing is very tough unless you're young or there's an overriding need, e.g. for dispersed families. At work virtual meetings or distance learning would need more features including screen sharing.
Huddle - no idea. There's probably more...
Is it evil? Of course. Granted Circles has all the good hippie open social web Googlers on board - Chris Messina (inventor of the hashtag), Joe Smarr, Chris Chabot and others - so I expect I could download a Circles server for my domain one day, or point my domain to Google, again. The rest more explicitly relies on Google magic, though I'll bet Google will provide means to liberate data, compete, etc. But, look at it this way. Google only wants you to tell them all your groups and all your interests. They won't do anything with that data except provide services for you of course, like advertising. The social graph they could get from this would keep them king in advertising, crushing the competition.
Will it fix the social web? Right now commenting and sharing takes a ninja to pick the right strategy to share things with the right people. I often get an email with a comment posted to a collab space where someone's posted a Google Doc. Where do I put my comments? I don't think this will change this problem. Don't know what could, though Salmon might, maybe, if it weren't so completely inpenetrable. Also I still think for the University we should start with one Circle - everyone at the University, including hangers on - and have a Twitter like following model allowing everyone to share purely our stuff. We could do like Google (and everyone else) and stick the status update field and results near the top of every University web page and it could work. The other circles might be several steps too far, or it could be the groups model we've been waiting for.
Is it good? Let's face it, it's the genius production of brilliantly talented engineers. Anyone seriously knocking it at this stage is arrogant, but the web can do that to you.
Will it work? When all's said and done I'm still a Google fanboy. I hope so.
Looking forward to hearing about this on TWiG tonight.
4 days ago