1) Lightroom saves all of your history states... forever!
Ever notice that when you're working in Lightroom you never actually have to save your image? In Photoshop we're always going to File > Save but not in LR. That's because Lightroom has a History panel in the Develop module (on the left side panel group). It automatically saves every single thing you do to your photos. The cool part is that unlike Photoshop (which discards your history when you quit the program), Lightroom saves this forever so you can always go back to it.
2) Lightroom's Backup feature only backs up your catalog, not your photos.
Don't forget that Lightroom's backup feature only backs up the catalog - not the photos. So if your computer crashed and you had your backup, you could reinstall Lightroom and revert to the backup you created from Lightroom. But you'd only have your catalog with all the "stuff" you've done to your photos. You wouldn't have your actual photos unless you've specifically backed them up separately (which is really easy if you follow Scott's advice on where to store your photos).
3) No matter what you do, if you shoot in raw, editing in Photoshop will create a copy of your image.
I hear this one a lot. People are surprised that after they go to edit a raw photo in Photoshop, there's a copy of the photo when they return to Lightroom. This will always happen. You can't change it because you can't edit the original raw photo in Photoshop. Lightroom has to render a copy of the image out and you'll have that copy (in PSD or TIFF format) when you return to Lightroom. Your raw photo is still there, by the way, and it will still have all of your Lightroom-related changes in it, but only the copy will contain any Photoshop edits you've done.
So there's my 3 add-ons to Scott's post. Take care!