A review from Lifehacker
Also - late breaking announcement from Google -it is stopping development of Notebook
Seven worthy Google Notebook Replacements - from CNET News.
Clipmarks is now on version 4. Note!!! It won't accept multiple set-ups form the same IP address which means that if you sit a class of 34 to all sign up at the same time, Clipmarks will lock you out (the same goes with Gmail).

What is the work-around? If you are working with one class - I would sign-up students a few at a time myself before the unit is about to begin - I ask the teacher to have the students email me and then I use their emails to sign them up.

Also - a homework assignment is for students to sign themselves up.

Lessons using clipmarks