When i come down and try to answer this question, I am invariably lost in thought about business model. Google is a data hungry model, which feeds, thrives and survives on data. User data. It all started with Google search engine which crawls through search to make it better.
Then came ORKUT, which did good , and integrated with google made it best thing. Then came facebook and swept the world. People started finding classmates, teachers , long lost friends and even parents of the late. People got into applications, and likes and then came chat. Now its video chat.
In the meantime, linkedIn and twitter came, but FB still kept its place. Google started its small piece of effort. Google Wave ... it waved off without any ripples. Then came Buzz , it still is an extra piece of noise in my gmail account. I hardly use it , but it keeps on adding to distraction. Well to the point, if Google Plus as of now is good.
As compared to facebook ,it has google chat in it. Like it . Not for long. If you enable it, and you have a gtalk / gmail chat running, then u will hear ping sounds more often. It has groups but not apps. One day u want to share a piece of news with a group, u post it for them. But if you think there is someone else who would be interested in that news, either you have to add him/ her up your group or let it go to all. Reposting and long procedures.
Video chat will take a long time, and there is no feature as group chat as in facebook. There are circles but they are not grouped. If you have an interest based group, then you can post them but not talk to them as in facebook.
The apps in google are not added, and even when they will be , i dont think it will be as wide as in FB. Facebook is used by millions today, and it does not require you to have a gmail account or a facebook account. It gives u a facebook account when u join. Will google plus give you that.
The idea for google plus would be a downturn since it will go to an already established network with very less features.
Now for instance , if I ask you today to delete your facebook account and start using google plus, would you do that if all your good friends are not on google plus.
Honest scare for those people who think a particular person will not add him/her up again will not do it.
As I finish , I will tell you one thing. Adding a person to your friend circle who have not joined google plus will not send them an invitation. Add a person to the circle, create a post and send them email. When the person receives email, he /she opens the post and joins the Google+