I think one of the main reasons why Google+ is doing so well is that they have taken time to produce a really well designed user interface. Facebook's UI is really poor in comparison. As a user, interaction should come natural and with Google+ it does. This is highlighted by positive interaction from 'non-techy' users. It is actually a pleasure to use. I could happily create and delete circles all day long :)
It used to be the case that the header and sub-header's were created from <h1> and <h2> tags on your website. That is why it is advised to only have one <h1> per page. I'm unsure whether or not that is still the case. Google are constantly changing how they display and rank results.
I would advise doing some research into search engine optimisation(SEO).
From what I've seen it has the potential to dethrone Skype but the major issue they have to overcome is that Skype is a household name when it comes to video calling. It's similar to how everybody still says 'Hoover' when really they should say vacuum cleaner.
It will take a lot to shift the mass market away from Skype.
If I were to add to it I stress the importance of reading books by different authors and publishers, even if they're about the same subject. This helps you get a much wider, well-rounded view and it often improves the learning experience.