I looked at the sites listed in the activity, looked up some tags, typed in my own search, etc. I then signed up for Delicious and was surprised that this is where my bookmarks could go and then not have any on a personal computer. Needless to say, I kept mine on my personal computer (I am not using my school computer to do the 23 things - had lost the key info to get into my home network -- anyway, that is another story).
I thought these sites were okay, probably a good way to discover what someone else has all ready tagged and therefore makes it an easier search for things.
As far as using this with students in Algebra II and PreCal classes, I really can't think of applications except maybe if a student needs additional help on a topic at home, this could be used to search the internet for explanations.