You admit you didn't even see the message, so you're engaging in pure speculation as to how you think it behaved, and then criticizing Apple for it.
> Changing what it's supposed to do
What it's supposed to do is provide a good natural language search of any and all information it has available to it. This is what millions of customers use it for, and this is what Yosemite enhanced. Now it has more information available to it. Just as I can ask Siri "what is planet of the apes?" and she'll tell me about the movie, now I can ask Spotlight for "planet of the apes" and learn about the movie. This is great! It's bringing functionality from iOS back to the Mac, in a form that's generally easier to use (speaking to Siri is not always convenient), and doing it in a way that seamlessly integrates with the existing functionality.
Afterwards, I did see it. Because it does show up if you hit cmd-space and then...you know...don't type. Which is insane, because of course I type as soon as I hit cmd-space, that's why I hit cmd-space.
I don't use Siri, either. I don't own an iPhone. You're more than welcome to have whatever internet-enabled hurf and/or durf you want, what I'm saying is that enabling it by default in what is a low-friction, high-usage tool that works on unconscious reflex is some real douchebaggery.
Insisting that Apple put scare dialogs in front of millions of users before doing something that is pretty darn safe is some real douchebaggery. Either it scares users into declining a feature that they'd probably actually appreciate having if they weren't required to click past a scary dialog, or it's one more step towards training users to unconsciously approve dialogs warning them of dangerous actions.
If you care so much about the possibility of a feature using the internet (as opposed to what would actually be a privacy violation, which is selling your information or queries to third parties, instead of, ya know, just using it to provide the functionality you're trying to use), then it's your responsibility to actually learn what this stuff is doing.
But you admitted to installing a brand new major OS update without reading anything at all about it. It's not Apple's fault that you chose to be so intentionally ignorant.
If you don't want the existing OS functionality to change, then don't install major OS updates. If you install major OS updates, then expect functionality to change. And the most cursory of searches would let you find out what's new and updated in the OS. Perhaps you should read the list to find out if any other functionality you use has been modified: http://www.apple.com/osx/all-features/
> Changing what it's supposed to do
What it's supposed to do is provide a good natural language search of any and all information it has available to it. This is what millions of customers use it for, and this is what Yosemite enhanced. Now it has more information available to it. Just as I can ask Siri "what is planet of the apes?" and she'll tell me about the movie, now I can ask Spotlight for "planet of the apes" and learn about the movie. This is great! It's bringing functionality from iOS back to the Mac, in a form that's generally easier to use (speaking to Siri is not always convenient), and doing it in a way that seamlessly integrates with the existing functionality.