Del.icio.us is the most commonly used link manager on the internet. Having a quicklink for your blog is pretty useful since not all have downloaded the firefox extension. I personally like to keep firefox as being _just_ a browser, given all the memory leaks from messy extension code and opt for only a tabbed browsing manager extension.
The code to add a url is simple enough:
Where example.com is your website.
You can add further fields to fill automatically. People usually add bookmarks very fast to reference them later, so having it become more convenient will make it more likely they finalize the process.
Replace foo with whatever your description and notes are. NOTE: It may be better to encode the string in url format. You can do so by using the urlencode() php function, or just typing it in in google and copy/pasting the q= part of the query string. I believe it will still work if you don't, but older browsers may have trouble viewing (like you care).
You can't automatically add the tags and description without their username. That part of the query string is automatically removed since del.icio.us believes (correctly) that people should write their own tags. Adding tags automatically still possible, which brings me to the next section
To make del.icio.us automatically add your site to their page when they click your del.icio.us link, you need a userbased site. Ask them from their del.icio.us username and store it in the database. Add a del.icio.us link specially crafted for members with a delicious username:
If they're logged in del.icio.us, it will automatically add the site without a prompt. This can be exploited if they use a framed page with constant redirects or popups, potentially adding a huge library of links, given they have your username.