Google promotes a new interface for Google Bookmarks, as part of Google Notebook. A similar interface can be accessed directly from Google Notebook if you click on "Unfiled bookmarks".
The old version of Google Bookmarks was integrated with the web history and allowed you to bookmark previously visited pages with one click. Another feature that's missing from the new version is full-text search, since bookmarks have been converted to notes.
On the bright side, the new interface is more responsive, it uses "infinite scrolling" to display the bookmarks and the notes can be formatted using a rich-text editor. Google Toolbar 5 (IE-only) lets you save the selected text from a page, which appears highlighted every time you visit the page.