As Jim said, all the adjustments are in the .lrcat file.
In my opinion, the things to backup when using a Lightroom workflow are (in order from highest priority to lowest priority):
1. Original raw files.
2. Lightroom catalog (.lrcat file).
3. Preview file (.lrdata file) and other LR settings.
Explanation:
If you lose #1 then you're stuck. Doesn't matter if you have everything else if you don't have the image.
If you lose #2, then it's a major bummer since you've lost all your work, but at least you still have the raw files and hence could reprocess your images if you had the time.
If you lose #3 (previews) then you can simply regenerate them automatically with LR. That'll slow you down a bit initially, but it's painless since you can do other productive stuff while waiting for the preview to rebuild. If you lose your settings (e.g., your presets) that's a pain but at least you didn't lose your image data.
As a side note, the built-in LR backup system will likely be improved in the future so the photographer doesn't have to keep all these distinctions in mind all the time.
