I gave up on my Perl/CGI scripted website for my kids' photos a couple of years back and moved them lock, stock and barrel to Flickr. It's a great service and I'm very happy with it. My initial upload was more than a thousand pictures, but I wanted to start out the right way so I tagged them all with people's names and so on. As you can imagine, this was pretty tedious, so I decided I would try and make sure I would never have to do that again. I did some digging around and came across the Flickr API. The authentication mechanism is a trifle cumbersome but some kind soul had already gone through the pain and posted a CC-licensed Python script that did most of the work. I messed around for a little bit and ended up with a little Python script that downloads an XML file for each photo in my photostream. The XML file contains all the metadata for the photo, including its title, description, tags, dates taken and posted. I run this script every week or so and it grabs the data for the pictures I've posted since the last time I ran it. This way I have all my photos' metadata in a parse-able form, so if Flickr should ever go away I can write something to parse the files and import them to whomever at that time.

I posted the script via TextMate's excellent Pastie service, in case anyone is interested. I had to strip out my Flickr API key and its shared secret (which you need in order to access the Flickr API) for obvious reasons, but it's simple enough to get your own from Flickr.

UPDATE April 3rd, 2008:
I had to update the script to pass the authorization token when looking up your username as it started returning "failed to find user". The updated script is linked above.