An opinion is a sentence that has the function to state a personal position about a certain matter. It generally reveals the truth from a person's (or a group of people) understanding and ideas about something, based on this person's (group of people) feelings and beliefs. It may not necessarily be a proven fact.
So, taking this in consideration, analysing sentence by sentence, we have:
Nancy couldn't make it today because she's visiting Leningrad - Fact.
One of these chips has more computing power than a roomful of old-style computers - Opinion!
Although President Reagan is stating a precise sentence, an apparent 'fact' here, it is not a proven fact.
But progress is not foreordained. - Opinion.
He's clearly stating his idea about 'progress'.
The key is freedom—freedom of thought, freedom of information - Opinion.
Again his idea about what 'the key' would be.
You know, one of the first contacts between your country and mine took place between Russian and American explorers - Fact.
Although not entirely precise, he's stating something that is generally believed to be true.
Perhaps most exciting are the winds of change that are blowing over the People's Republic of China - Not an opinion nor fact.
He's not saying a complete trustworthy information here, but he's not also demonstrating a straight opinion either. When stating something that may or may not be true (through the 'Perhaps', in this case), you are in a certain way saying that you don't have an opinion about that yet, but you're provoking a discussion (or at least the thoughts) towards one.
And that's why it's so hard for government planners, no matter how sophisticated, to ever substitute for millions of individuals - Opinion.
