I like them though they are not my favourite site. It is quite convenient to be able to bookmark and classify with some tags. It's very easy when a blogger has del.ico.us links on thier posts. One improvement I would like is an easy way to search by multiple tags.
I like it. I use it as a back-up, in case my computer ever crashes, so I don't lose all the good links I have collected over the years. A couple other good sites (there are many more) are Blinklist and Shadows.