The practical stuff first.
In February 2009, inspired by Pete Prodoehl, I set up my own version of scuttle, an open source del.icio.us clone, and hacked it to auto-post my bookmarks to my del.icio.us account using the php-delicious library.
I have finally pushed this to github. My change is literally about ten lines of code, although as my delicious account testifies, it has bugs that I haven’t been bothered to fix. It is currently version 0.7.4 of scuttle, and I plan on merging it to the latest 0.9 in a day or two.
Update: actually it looks like I set this up in 2006, way before I remember!