del.isio.us

I have been using del.isio.us for several months; ever since all of my favourites were inadvertantly wiped on our home computer (twice).
It's so easy to use and is really useful when you use several computers like we do. I use it for work, study and personal use.
It's much easier to keep track of one set of favourites than several, and trying to update in different places.
Being able to add your own set of tags is an advantage over just using the favourites folders also.
Quite often, things fit into more than one category.
I'm sure I'm only using the basics of the software, but like a lot of other things on this course, it's useful to know there are more applications of it that I can get around to when time allows.