"you would probably also love the ability to tag each of your photos with keywords".
I know this is possible in Lightroom. Two problems however: (1) I already did that and want that exported over to Light room somehow. I did scan the Internet and there are some ways but most are 'buggy' (admittedly: due to problems on the Picasa side of things. (2) In Picasa, I have also marked WHERE the faces are (that's standard there). In Lightroom I can only add/import keywords (in this case: who is or are in the picture) but now WHERE they are... Imagine an old school photo with 30+ kids... In Picasa I named all the 'heads', in Lightroom I guess that's not possible, right?
Now if Lightroom is a program focused mainly on 'managing' photo collections, wouldn't this be at least an 'important' need-to-have feature???