There are many ways to add notes to Google Notebook: you can visit google.com/notebook or click on "My notebooks" from any Google search results page. To add excerpts from web pages, you need an extension: Google Toolbar 5 for IE or Google Notebook for Firefox. But what happens if you use a browser like Safari or if you aren't allowed to install add-ons?
Google Notebook bookmarklet is a lightweight alternative that doesn't require installation. You just drag and drop a link to your browser's links bar or bookmark the link. To copy some content from a web page to a notebook, just select the text and click on "Note this".
For some reason, Opera can only view notebooks, so this bookmarklet can't be used to add notes.
Related:
Useful Google bookmarklets
{ via Google Notebook Blog }