open source
Here are a couple of greasemonkey scripts that I find usefull
I don't like the way that del.icio.us represents the number of other people who have the same link bookmarked as you do. So this script changes this:

into this:

Bloglines is a great service, but it can get very hard to see what you want if you have a feed with a lot of noise. This script makes it easier to scroll through a bunch entries quickly, finding what you need without having to read every headline by highlighting the text you specify with regexps.