For one thing, I'm discovering that the collection of postcards on my hard drive is incomplete: my Postcrossing wall shows several cards that I never scanned in. Those were scanned in and uploaded to Postcrossing by the people who sent them, so when I registered the card, the image of it just showed up and I had no need to scan it in. Now I'm going through my postcard album and a large black box filled with old postcards, digging out the missing pieces of my collection and scanning those in appropriately.
I deleted my collection of postcards in Picasa because I just couldn't get the folder renamed appropriately. It was one thing online and another name on my computer, so that made it tricky to upload and keep in sync. I just did away with it by deleting all online albums, renaming the folder on my hard drive, and reuploading it all over again. Fortunately, geotagging the postcards in Picasa on my machine automatically geotags them in the online Picasaweb album. This is important because it cuts down on a step: when I go into Postcrossing and look up the postcards I've received and the users who sent them, there's a link to the users' hometown in Google Maps, and clicking on that provides me coordinates that I can feed right into Picasa. Now I can see a map of the world and an array of postcards from their nation and town of origin, and that's all I really wanted.
Next, I'll see how difficult it would be to link this to Google Earth, however it does that.