you'll find many people having issues with how they share posts and messages +Jean Fisher
its really quite simple as a rule all posts should only be Public and thats it.
I get too many posts sent to me by bloggers that post public and then add in their circles. When this is done in essence they are spamming those they send notifications too.
Circles are designed so you can reach certain people with messages/posts that are directed at that group, not as an add on to public. Circles are also great so you can check out certain groups in the stream to see what they've been up to, its really a great way to keep people that are important to you in groups that are easily reached.
What you're seeing in your feed is either people that share incorrectly or friends that have plussed one the post, this will also randomly send posts to your feed as +1's acts like a recommendation.
As for your PM it sounds like you did them correctly.