So the actual technical bit wasn't too hard, I just used Flickr::API (and the Flickr API docs) and Flickr::Upload. I actually use tags on my photos, so that's handy. The small script I ended up with to sync the photos is made of up two main subroutines, one to decode the XML returned from Flickr and the other to upload a photo. It's just nice simple glue code.
But what's it like for users? Well, Flickr does quite a bit of metadata, so you can see my most popular tags, which I initially thought was a bit of a gimmick, but is quite neat. Also, I get to see the most viewed / favourited / commented photos, which is nice.
I'm still not sure I'm happy about Flickr using Flash to show plain photos. Time for a Flickr Lite?