OK... that video sounds like they don't know what they're talking about.
First... PC or Mac, Lightroom is the same. I've got both here. It's basically the same experience, it just runs a tad slower on the Mac. So PC users should share their experiences in this thread as well.
Now.. Lightroom is non destructive. When you make adjustments to a file it's not really editing the file, it is showing you a preview of the settings you're applying. THen when you export the file out it applies those settings and saves a "finished" file. So when you make all those adjustments to a RAW file and export it as a jpeg it is not doing a single thing to your RAW file. No matter where you save that jpeg. If you don't export the file as a jpeg (or other format) it will keep the adjustments you've made to the RAW file in your Lightroom Library. But again, it hasn't actually made any changes to the file and you can reset to the original state at any time.
I export my "finished" images to a separate folder, but that's totally a personal preference thing. Put them where you want them. As long as you know where they are you're good.
Take the photos out of iPhoto.... OK, you don't have to take anything out of anywhere to use Lightroom. You simply tell Lightroom to import the files from their original location. Go to the library pane and click the plus sign to add folders and then find what you need in the Finder window. It's very simple. It will come up with a window that shows what you're about to import. Add any tags you want and import. The main drawback from doing this if you've been using iPhoto is that you will end up with a thumbnail of each image as well because of how iPhoto works (or at least that's how it used to work, they may have changed it since i quit using it)