Google Notebook or del.icio.us?
Google Notebook groups notes (content excerpt or comment, title, and link) into optional sections, thence into notebooks, thence into a collection of notebooks.
del.icio.us associates tags with links (title, comment or copied excerpt, and link) instead of grouping them. This allows more flexible link sets than groupings, and more of them.
Google Notebook's shallow hierarchy does not let you know if you have the same link in multiple notebooks, or in multiple sections within a notebook. Even if your notebook is shared, Google Notebooks (as far as I've seen) does not let you know what other public notebooks contain your link, so you can't see what related content other users found. It would not surprise me to learn that notebook agglomeration is planned, though.
Google Notebook's groupings do allow more efficient control over sharing links. del.icio.us links must be shared or unshared one at a time. I'm not sure why you would want to, but Google Notebooks allows you to share a link in one notebook, but leave it unshared in another.
Controlled sharing would be useful for cases where you want to share the results of your research with a only few other people (eg, confidential research on personal medical conditions). Google Calendar has a good interface for this: the owner publishes a calendar to another user by Google account name; then Google Calendar incorporates these entries into the other user's events.
Google Tools I Use
I used Google Reader, but switched to Rojo (better tags, and better feed interaction); Google's personal home page, but switched to Pageflakes (multiple pages, and multiple items of the same type on a page); used Blogger, but switched to WordPress (better templates and widgets; more control over posts, pages, and categories). In each case, Google provided an adequate startup tool, but I found its replacement worked more the way I wanted.
Kanso Carries the Day
In practice, del.icio.us wins over Google Notebook, JetEye, and Clipmarks, since its browser extension is simpler. I can use its interface (two bookmarklets) with the alpha releases of Bon Echo. The applications for the other two services check the version of the browser that's running, and don't recognize Bon Echo, so they won't run. I'm sure they'll all recognize the new Firefox when it's official, but I would rather use a tool that does not inhibit early adoption of other tools.