I am not one of the lucky invitees, but I'm waiting to see what Google+ is all about. I hear great things, but I'll believe it when I see it. Google has a lot going for it, but they are nowhere near the end-all answer to everything.
I remember a decade ago when Yahoo! was the search engine of choice. Then Google came around, and for some reason, they took off. Almost everyone I knew switched to Google, but I couldn't understand why. I always seemed to get better search results from Yahoo, and Google always seemed to return more results than I needed.
However, over the past decade, Google has improved their search engine (due to more popularity?), and Yahoo's seems to have declined (I don't understand how that happened). A couple of years ago, I finally gave up on Yahoo, and now I almost exclusively use Google.
I still go to Yahoo for news. They have that cute news box on their home page that cycles through some 48 popular news stories. (Though I hate that it often cycles to the next article when you're about to click on a link.)
I prefer Yahoo Mail over Gmail, because the interface is easier to use. Yahoo has a preview screen where you can click on an email and see in the window below it. Gmail doesn't seem to have this. I hate having to click on a gmail to read it, and then click the back button to go back to my inbox. An alternate nice feature would be to allow for opening each email in a separate tab. Then I could go through my emails much more quickly.
As you can tell, I use Blogger (run by Google). The posting interface is fun to use, but is very buggy. The cursor doesn't always blink where its supposed to. Sometimes it jumps to the very beginning of the article I'm editing. And what you see isn't what you always get. I almost always have to fight between "Preview" and editing until it looks right.
Supposedly, Blogger is going away at the end of this month to be replaced by a feature of Google+. I don't know what that means, but my guess is that my posts will still exist, though my links may be out of whack. We'll see how they handle the migration.
Google Buzz looks to be nowhere near Facebook or Twitter. Buzz looks like a Facebook wannabe with no privacy controls.
Judging by what Google has put out in the past, I wouldn't be surprised if Google+ is buggy. Though, it would be cool if it knocks Facebook out of the water. After all, Facebook is very buggy, and its privacy controls are confusing. (I hear the Google+ privacy controls are even more confusing, and that people in your "circle" can still share your post with whomever they want. We'll see when it comes out.)
Regardless, if I were Facebook, I'd be shaking in my boots. First, it was Classmates, and then MySpace, and now Facebook. Google+ could be next. For better or for worse--get ready for it!