For now, I have one big California LR catalog and then one for each major area like Indonesia, Philippines etc. Since I pretty much only rate my pics as zero, one or two stars, finding a "best" one is pretty tough. I am hoping that LR 3 will let me actually make reasonably nice slideshows like Fotomagico but so far I am not smart enough to figure out how to make that happen.
Hey Bill,
I can help a little with the keywording, although a twelve year old might find a faster way. In the Library Grid view select all the images you want to add keywords to. (Select the first image and scroll to the bottom and shift select the last one) On the bottom right click "Sync Metadata" The sync screen will pop up and if you can scroll to the bottom you'll see the keyword section. Select the box next to keyword and type in any keyword you want on all these images. (Make sure all the other boxes like copyright are uncheckedand are not filled). When your all set hit the "Synchronise" button and you have just added your keyword(s) to all the selected images. If you select your Catalog and "all photographs" you can add a keyword(s) to every pic on your machine in a few seconds. 
DANGER, this only works if you have no other keywords assigned to the image you first selected, other wise you will be copying those key words to all the selected images too.
Give it a try, the Sync metadata button is great for all kinds of uses.
Keeping your catalogs seperate by major location makes sense to me too. I misunderstood, when you said a catalog for each divesite. I had visions of hundreds clogging up the works.
Cheers,
Steve