after seeing it referred to many many times, glancing at it once in a while, and basically ignoring it, ive finally sat down to take a look at del.icio.us and ive got to say, its pretty sweet.
and don't forget the firefox extension to make it even easier to make links. or other nutr.itio.us ideas.
not that having online bookmarks is that new of an idea. honestly the only cool thing about this is the ability to add "tags" to everything. that is, one bookmark can have more than one category.
for example, a link to MarsEdit might be tagged as "blogging" and "osx"
so what? so you don't have to maintain the standard view of your bookmarks in a hierarchical manner, allowing you to find your links faster as you spend less time thinking "ok, now what category does this fit the best under?" because it can fit in any category, perfectly or not.
this concept also isn't that new, but for some reason hasn't caught on too much yet. the programs that use it effectively, i consider very good: GMail, Photoshop Album, Flickr, etc (more?)
this whole concept of mapping one object to several names is very useful. our brains work that way, we are not strictly hierarchical in organizing our thoughts. it reminds me of a better way of organizing files a la kurzweil's brain (java applet) and the much-hyped MS Longhorn WinFS (i think). ive heard that BeOS had a similar filesystem for a while. not sure if that is true anymore.
these tools are so intuitive and easy to use, its just a matter of time before more pop up.