Today I received a Google+ invite from @HugoAhlberg. My first impression was, wow this is slick! It feels stable, there are some great animations here and there as used in the composition of groups (circles).
It looks a lot like FaceBook, mainly the layout structure and posting messages on your "wall"/"stream" are a lot alike. The big difference is the way you share things, you share things with your personal composed circles. Personally I find this a very nice thought, this makes it more private. So when you are posting a message you will get a drop down list to select with which circles you like to share it.
What I also noticed that there is a "Following" circle, it seems that there is a "follow" feature just like Twitter. You will be able to place interesting people into a circle and see what they have to say. On the other hand, people can also follow you and read all the posts that you posted publicly.
There is also a feature called "Sparks", these are Google searches that you can save. Suppose you find "web design" an interesting topic, you could fill that in as search query. Then add it to your "Sparks" list and get an overview of all the news about that topic.
In short Google+ is nice and has great potential.