I think del.icio.us is missing a trick. Del.icio.us, for those who don't know, is a service that allows you to create an account to store your favourite links to websites so that you (and anyone else) can find them. It also groups these up by 'tags' (categories) and let's everyone know how many of the people who use the service have that same link in their collection.
What it doesn't do, is let people visit the del.icio.us homepage and search the links. So what? You can wander about clicking on category names and find the links you're after instead. Well, what are they creating? Essentially they're creating a portal, like yahoo, or a directory like DMOZ, but with thousands of contributing editors, all providing quality links (they've checked them out, they've found them useful enough to bookmark). Now take into account the ability to add 'notes' to these links and you have a great set of contextual data. Now, if you could search both of these, you'd have a database of high quality links, with plenty of real user (i.e. not a computer ranking system) recommendations, feedback and filtering. We are all looking for ways to get better, more relevant results when we search (the whole reason for Google taking and maintaining number 1 spot in the search market was because they returned the best results) and this is a way to get them. I'm not saying it'll replace Google, because every search won't be covered, and neither would every site, but as a place to get great results it surely couldn't be beaten.
I think the people behind del.icio.us would be well advised to implement a search facility.