The 5,000 Limitation On Google Plus: A Good Thing
If you want to interact with a million people, that is what Twitter is for. I am glad Google Plus has that limitation. So people are more careful in terms of who they add to their circles.
Facebook also has that limitation. Facebook perhaps is the inspiration to that Google number. If you want to interact with more than 5,000 people, well, there are Facebook Pages you can create.
I think a limitless number of people can follow you on Google Buzz. That would be the Google version of Facebook Pages. I think there is no limit to how many followers you can have on Google Buzz. But I don't know for sure.