del.icio.us, the social bookmarking service, turned two yesterday, and I wish it the very happiest of birthdays. How do I love del.icio.us? Let me count the ways:

1. The first, and best, attraction of del.icio.us is accessing my bookmarks from any computer in the world and from any browser. I can't count how much time I have wasted in the past shuttling and consolidating bookmark files between browsers and computers. Aside from a few toolbar bookmarks and bookmarklets, I don't use browser bookmarks at all anymore.
2. I have come to rely on the the Inbox feature for making web discoveries. By subscribing to their del.icio.us lists, I now have Eastgate's Mark Bernstein, But She's a Girl, The Primary Vivid Weblog's Dan Dickinson, Donut Muse's Chris Fazio, Mamamusing's Liz Lawley, 43 Folders's Merlin Mann, Doing Something Different's Doug Miller, Decafbad's Les Orchard, and jill/txt's Jill Walker all surfing the web for me. In fact, I found the del.icio.us birthday announcement this way (via del.icio.us/merlinmann).
3. del.icio.us tags are the first method of organizing web links that has ever really worked for me. Browser bookmark lists have always degenerated into either interminable scrolling or impossible-to-navigate hierarchies (and sometimes both), so that bookmarking a page was tantamount to forgetting it. Tags, by contrast, are personal, flexible, and endlessly reconfigurable. I don't have to agonize about where to put a particular link; if it needs to be in more than one place, I just add a tag. If I don't like how I filed it, I can just delete or rename or merge some tags.
4. They have continued improved the usability of tags by introducing new features like "cloud view" (which i have discussed before) and "bundles" (more on this later).
5. With the del.icio.us plug-in for Quicksilver, I can search my bookmarks and copy a URL without ever opening a browser.
6. I can subscribe to virtually any del.icio.us page (from the main del.icio.us page to my inbox to a fancy combined search for multiple tags within a specific subsection of the del.icio.us universe) via an RSS feed.
7. I can get an HTML feed of del.icio.us pages for inclusion in other web pages (like the Bookmark list in the sidebar of Donut Age). More recently they have added support for javascript-powered "linkrolls."

I mentioned bundles above. They were introduced back with the "cloud view" in June, but I've only recently begun playing with them. Briefly, bundles are yet another way to make large numbers of tags more manageable. At first glance, I thought they were a step toward fixed hierarchy, but like tags themselves, bundles are highly flexible. A tag can be assigned to any number of bundles (or none), so there's no need to fret about where a tag "really belongs." And you can toggle bundle-view on and off and combine it with cloud-view or not, providing many ways of visualizing your tags.

In short, I love del.icio.us because it is so adaptable. It can be put to many purposes, and new capabilities are being added constantly, but at its core it remains elegantly straightforward and simple. May it enjoy many more birthdays!