I've been using del.icio.us for quite a while now and have found it to be way more than bookmark voyeurism. Here are some useful tips that are good for folks in PR agencies like me:

1. Create an ad hoc, organic directory of blogs. I tag Singapore blogs I find "sgblog" in hopes of building my little own localsphere.
2. Tag press releases you place on PR wires by clients so you have an easy access list of'em all.
   
3. Capture and tag online clippings for clients. Beat that Excel spreadsheet! (Kudos to John Kerr, Edelman for this one)
4. Tag your client's competition and measure share of voice against the above tip. The tag cloud is an easy way to see who's in the lead.
   
5. Bookmark items you find for your colleagues and friends. Way easier than sending the link by email.
6. Great reference for industry intelligence and research. Especially when the browser history forgets the link.
   
7. Subscribe to http://del.icio.us/tag/pr.

Add your tips in the comments. =)