Re: adjustments to RAW files, Dave is correct, there is no separate file containing the adjustments, like other RAW editors do. However, any changes you do CAN be undone. You can revert an image back to its original state (reset all changes) or you can reset individual adjustments ... hold ALT + click the relevant button, e.g. alt+saturation button resets the saturation level to the "as shot" level.
Re: attaching keywords at import, I agree with Stepheno ... I tried it once, but forgot to reset the keywords at the import stage for the next group of images ... result was that all the photo's in that import had the wrong keywords
Therefore, I recommend Stepheno's method of attaching keywords later.
I've used LR quite a bit now, + previously made some comments on my findings, which I hoped would be of use to other members ... they are mainly in an earlier thread called [something-something] Lightroom
