I've just had some great fun trying to add a browser Favicon to a website I am working on. We don't get much client demand for these, so it's been a while since I've had the task of creating one.
I decided to read-up on Wikipedia and on W3.org before-hand and followed all of the suggestions therein. The result? Icons which show in Firefox, Safari and Opera but not IE 7 or 6. What a surprise!